python kivy android app crashes after running apk on mobile device

I was trying to develop an android app using the kivy python framework. The program connects with a remote mysql database. A part of the code (registration and login page) was tested in pyCharm and found to be working perfectly. For converting to an android app, Ubuntu 19.10 OS running on Oracle VM VirtualBox was used. APK file was obtained by running command buildozer android debug. But on running the command buildozer android deploy run, the following output with error message comes and app crashes.

> List of devices attached
> ZX1PC222GV device
> Run on ZX1PC222GV
> Run '/home/nirmal/.buildozer/android/platform/android-sdk/platform-tools/adb shell am start -n org.test.kkfoodies/org.kivy.android.PythonActivity -a org.kivy.android.PythonActivity'
> Cwd /home/nirmal/.buildozer/android/platform
> Starting: Intent { act=org.kivy.android.PythonActivity
cmp=org.test.kkfoodies/org.kivy.android.PythonActivity }
> Error type 3
> Error: Activity class {org.test.kkfoodies/org.kivy.android.PythonActivity} does not exist.
> Application started

Here is my buildozer.spec file

[app]
# (str) Title of your application
title = KK Foodies
# (str) Package name
package.name = kkfoodies
# (str) Package domain (needed for android/ios packaging)
package.domain = org.test
# (str) Source code where the main.py live
source.dir = .
# (list) Source files to include (let empty to include all the files)
source.include_exts = py,png,jpg,kv,atlas
# (list) List of inclusions using pattern matching
#source.include_patterns = assets/*,images/*.png
# (list) Source files to exclude (let empty to not exclude anything)
#source.exclude_exts = spec
# (list) List of directory to exclude (let empty to not exclude anything)
#source.exclude_dirs = tests, bin
# (list) List of exclusions using pattern matching
#source.exclude_patterns = license,images/*/*.jpg
# (str) Application versioning (method 1)
version = 1.0
# (str) Application versioning (method 2)
# version.regex = __version__ = ['"](.*)['"]
# version.filename = %(source.dir)s/main.py
# (list) Application requirements
# comma separated e.g. requirements = sqlite3,kivy
requirements = python3,kivy
# (str) Custom source folders for requirements
# Sets custom source for any requirements with recipes
# requirements.source.kivy = ../../kivy
# (list) Garden requirements
#garden_requirements =
# (str) Presplash of the application
#presplash.filename = %(source.dir)s/data/presplash.png
# (str) Icon of the application
#icon.filename = %(source.dir)s/data/icon.png
# (str) Supported orientation (one of landscape, sensorLandscape, portrait or all)
orientation = portrait
# (list) List of service to declare
#services = NAME:ENTRYPOINT_TO_PY,NAME2:ENTRYPOINT2_TO_PY
#
# OSX Specific
#
#
# author = © Copyright Info
# change the major version of python used by the app
osx.python_version = 3
# Kivy version to use
osx.kivy_version = 1.9.1
#
# Android specific
#
# (bool) Indicate if the application should be fullscreen or not
fullscreen = 0
# (string) Presplash background color (for new android toolchain)
# Supported formats are: #RRGGBB #AARRGGBB or one of the following names:
# red, blue, green, black, white, gray, cyan, magenta, yellow, lightgray,
# darkgray, grey, lightgrey, darkgrey, aqua, fuchsia, lime, maroon, navy,
# olive, purple, silver, teal.
#android.presplash_color = #FFFFFF
# (list) Permissions
#android.permissions = INTERNET
# (int) Target Android API, should be as high as possible.
#android.api = 27
# (int) Minimum API your APK will support.
android.minapi = 21
# (int) Android SDK version to use
#android.sdk = 20
# (str) Android NDK version to use
#android.ndk = 17c
# (int) Android NDK API to use. This is the minimum API your app will support,         it should usually match android.minapi.
#android.ndk_api = 21
# (bool) Use --private data storage (True) or --dir public storage (False)
#android.private_storage = True
# (str) Android NDK directory (if empty, it will be automatically downloaded.)
#android.ndk_path =
# (str) Android SDK directory (if empty, it will be automatically downloaded.)
#android.sdk_path =
# (str) ANT directory (if empty, it will be automatically downloaded.)
#android.ant_path =
# (bool) If True, then skip trying to update the Android sdk
# This can be useful to avoid excess Internet downloads or save time
# when an update is due and you just want to test/build your package
# android.skip_update = False
# (bool) If True, then automatically accept SDK license
# agreements. This is intended for automation only. If set to False,
# the default, you will be shown the license when first running
# buildozer.
# android.accept_sdk_license = False
# (str) Android entry point, default is ok for Kivy-based app
#android.entrypoint = org.renpy.android.PythonActivity
# (str) Android app theme, default is ok for Kivy-based app
# android.apptheme = "@android:style/Theme.NoTitleBar"
# (list) Pattern to whitelist for the whole project
#android.whitelist =
# (str) Path to a custom whitelist file
#android.whitelist_src =
# (str) Path to a custom blacklist file
#android.blacklist_src =
# (list) List of Java .jar files to add to the libs so that pyjnius can access
# their classes. Don't add jars that you do not need, since extra jars can     slow
# down the build process. Allows wildcards matching, for example:
# OUYA-ODK/libs/*.jar
#android.add_jars = foo.jar,bar.jar,path/to/more/*.jar
# (list) List of Java files to add to the android project (can be java or a
# directory containing the files)
#android.add_src =
# (list) Android AAR archives to add (currently works only with sdl2_gradle
# bootstrap)
#android.add_aars =
# (list) Gradle dependencies to add (currently works only with sdl2_gradle
# bootstrap)
#android.gradle_dependencies =
# (list) add java compile options
# this can for example be necessary when importing certain java libraries     using the 'android.gradle_dependencies' option
# see https://developer.android.com/studio/write/java8-support for further     information
# android.add_compile_options = "sourceCompatibility = 1.8",     "targetCompatibility = 1.8"
# (list) Gradle repositories to add {can be necessary for some         android.gradle_dependencies}
# please enclose in double quotes 
# e.g. android.gradle_repositories = "maven { url     'https://kotlin.bintray.com/ktor' }"
#android.add_gradle_repositories =
# (list) packaging options to add 
# see https://google.github.io/android-gradle-    dsl/current/com.android.build.gradle.internal.dsl.PackagingOptions.html
# can be necessary to solve conflicts in gradle_dependencies
# please enclose in double quotes 
# e.g. android.add_packaging_options = "exclude 'META-    INF/common.kotlin_module'", "exclude 'META-INF/*.kotlin_module'"
#android.add_gradle_repositories =
# (list) Java classes to add as activities to the manifest.
#android.add_activites = com.example.ExampleActivity
# (str) OUYA Console category. Should be one of GAME or APP
# If you leave this blank, OUYA support will not be enabled
#android.ouya.category = GAME
# (str) Filename of OUYA Console icon. It must be a 732x412 png image.
#android.ouya.icon.filename = %(source.dir)s/data/ouya_icon.png
# (str) XML file to include as an intent filters in <activity> tag
#android.manifest.intent_filters =
# (str) launchMode to set for the main activity
#android.manifest.launch_mode = standard
# (list) Android additional libraries to copy into libs/armeabi
#android.add_libs_armeabi = libs/android/*.so
#android.add_libs_armeabi_v7a = libs/android-v7/*.so
#android.add_libs_arm64_v8a = libs/android-v8/*.so
#android.add_libs_x86 = libs/android-x86/*.so
#android.add_libs_mips = libs/android-mips/*.so
# (bool) Indicate whether the screen should stay on
# Don't forget to add the WAKE_LOCK permission if you set this to True
#android.wakelock = False
# (list) Android application meta-data to set (key=value format)
#android.meta_data =
# (list) Android library project to add (will be added in the
# project.properties automatically.)
#android.library_references =
# (list) Android shared libraries which will be added to AndroidManifest.xml     using <uses-library> tag
#android.uses_library =
# (str) Android logcat filters to use
#android.logcat_filters = *:S python:D
# (bool) Copy library instead of making a libpymodules.so
#android.copy_libs = 1
# (str) The Android arch to build for, choices: armeabi-v7a, arm64-v8a, x86,     x86_64
android.arch = armeabi-v7a
#
# Python for android (p4a) specific
#
# (str) python-for-android fork to use, defaults to upstream (kivy)
#p4a.fork = kivy
# (str) python-for-android branch to use, defaults to master
#p4a.branch = master
# (str) python-for-android git clone directory (if empty, it will be     automatically cloned from github)
#p4a.source_dir =
# (str) The directory in which python-for-android should look for your own build recipes (if any)
#p4a.local_recipes =
# (str) Filename to the hook for p4a
#p4a.hook =
# (str) Bootstrap to use for android builds
# p4a.bootstrap = sdl2
# (int) port number to specify an explicit --port= p4a argument (eg for bootstrap flask)
#p4a.port =
#
# iOS specific
#
# (str) Path to a custom kivy-ios folder
#ios.kivy_ios_dir = ../kivy-ios
# Alternately, specify the URL and branch of a git checkout:
ios.kivy_ios_url = https://github.com/kivy/kivy-ios
ios.kivy_ios_branch = master
# Another platform dependency: ios-deploy
# Uncomment to use a custom checkout
#ios.ios_deploy_dir = ../ios_deploy
# Or specify URL and branch
ios.ios_deploy_url = https://github.com/phonegap/ios-deploy
ios.ios_deploy_branch = 1.7.0
# (str) Name of the certificate to use for signing the debug version
# Get a list of available identities: buildozer ios list_identities
#ios.codesign.debug = "iPhone Developer: <lastname> <firstname> (<hexstring>)"
# (str) Name of the certificate to use for signing the release version
#ios.codesign.release = %(ios.codesign.debug)s
[buildozer]
# (int) Log level (0 = error only, 1 = info, 2 = debug (with command output))
log_level = 2
# (int) Display warning if buildozer is run as root (0 = False, 1 = True)
warn_on_root = 1
# (str) Path to build artifact storage, absolute or relative to spec file
# build_dir = ./.buildozer
# (str) Path to build output (i.e. .apk, .ipa) storage
# bin_dir = ./bin
#    -----------------------------------------------------------------------------
#    List as sections
#
#    You can define all the "list" as [section:key].
#    Each line will be considered as a option to the list.
#    Let's take [app] / source.exclude_patterns.
#    Instead of doing:
#
#[app]
#source.exclude_patterns = license,data/audio/*.wav,data/images/original/*
#
#    This can be translated into:
#
#[app:source.exclude_patterns]
#license
#data/audio/*.wav
#data/images/original/*
#
#    -----------------------------------------------------------------------------
#    Profiles
#
#    You can extend section / key with a profile
#    For example, you want to deploy a demo version of your application     without
#    HD content. You could first change the title to add "(demo)" in the name
#    and extend the excluded directories to remove the HD content.
#
#[app@demo]
#title = My Application (demo)
#
#[app:source.exclude_patterns@demo]
#images/hd/*
#
#    Then, invoke the command line with the "demo" profile:
#
#buildozer --profile demo android debug

The python file is given below.

from kivy.app import App
from kivy.properties import ObjectProperty
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.relativelayout import RelativeLayout
from kivy.uix.scrollview import ScrollView
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.uix.togglebutton import ToggleButton
from kivy.uix.checkbox import CheckBox
from kivy.uix.spinner import Spinner
from kivy.properties import NumericProperty   #, ListProperty
from kivy.uix.textinput import TextInput
from kivy.uix.popup import Popup
# from kivy.uix.bubble import Bubble
from kivy.uix.image import Image
from kivy.lang import Builder
import MySQLdb
import hashlib, binascii, os
from kivy.uix.screenmanager import ScreenManager, Screen
# from datetime import date, timedelta
from kivy.uix.popup import Popup
from datepicker import DatePicker  # , CalendarWidget
import base64
from functools import partial
import textwrap
# import numpy as np
# import cv2
# import io
# import PIL.Image
#_imaging = PIL.Image.core
# from PIL import Image
# from PIL.Image import core as _imaging
# import Image
# import sys
# import cStringIO
# import timepicker
# from kivy.garden.circulardatetimepicker import CircularTimePicker
from kivy.core.window import Window
# Window.clearcolor = (204/255, 1, 244/255, 0)
class ScreenManagement(ScreenManager):
pass
myname = ''
selldate = ''
roomno = ''
try:
dbconnect = MySQLdb.connect("IP", "username", "password",
"dbname")  
except (MySQLdb.Error) as e:  # , MySQLdb.Warning
print("Can't connect to database", e)
exit()
# return 0
# If Connection Is Successful
# print("Connected")
crsr = dbconnect.cursor()
class ListHeader(Button):
def __init__(self, **kwargs):
super().__init__(**kwargs)
# bcolor = ListProperty([1, 1, 1, 1])
class ListCell(Label):
def __init__(self, **kwargs):
super().__init__(**kwargs)
# bcolor = ListProperty([1, 1, 1, 1])
class DbCon:
def __init__(self, **kwargs):
super().__init__(**kwargs)
def get_row(self, uname):
query = "SELECT username, passwordh, emp_no, full_name, room_no, authorisation_flag FROM residents WHERE username = '%s" % uname + "'"
# query = "SELECT userid, pass, mob, fname, lname, mailid FROM login_data WHERE userid = '%s" % uname + "'"
print(query)
crsr.execute(query)
return crsr.fetchone()
def add_row(self, username, password, empnum, fullname, roomnum):
hashedpwd = self.hash_password(password)
print(hashedpwd)
sqlquery = "INSERT INTO residents (username, passwordh, emp_no, full_name, room_no) VALUES (%s, %s, %s, %s, %s)"
insert_values = (username, hashedpwd, empnum, fullname, roomnum)
crsr.execute(sqlquery, insert_values)
dbconnect.commit()
print(crsr.rowcount, " record inserted.")
def hash_password(self, password):
"""Hash a password for storing."""
salt = hashlib.sha256(os.urandom(60)).hexdigest().encode('ascii')
pwdhash = hashlib.pbkdf2_hmac('sha512', password.encode('utf-8'),
salt, 10000)
pwdhash = binascii.hexlify(pwdhash)
return (salt + pwdhash).decode('ascii')
class LoginWindow(Screen):
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.db = DbCon()
def validate_user(self):
user = self.ids.username_field
pwd = self.ids.pwd_field
info = self.ids.info
global myname, roomno
uname = user.text
passw = pwd.text
if uname == '' or passw == '':
info.text = '[color=#FF0000]username and/ or password required[/color]'
else:
row = self.db.get_row(uname)
if row == '':
info.text = '[color=#FF0000]Invalid Username and/or Password[/color]'
else:
stored_passwd = row[1]
myname = row[3]
roomno = row[4]
print(stored_passwd)
print(passw)
if self.verify_password(stored_passwd, passw):
# if stored_passwd == passw:
if row[5] == 1:
info.text = '[color=#00FF00]Logged In successfully!!![/color]'
self.parent.current = 'menu'
else:
info.text = '[color=#FF0000]Sorry, you are not authorised. Please collect authorisation details from administrator.[/color]'
else:
info.text = '[color=#FF0000]Incorrect Password[/color]'
def verify_password(self, stored_password, provided_password):
"""Verify a stored password against one provided by user"""
salt = stored_password[:64]
stored_password = stored_password[64:]
pwdhash = hashlib.pbkdf2_hmac('sha512',
provided_password.encode('utf-8'),
salt.encode('ascii'),
10000)
pwdhash = binascii.hexlify(pwdhash).decode('ascii')
print(pwdhash)
return pwdhash == stored_password
class RegisterWindow(Screen):
def __init__(self, **kwargs):
super().__init__(**kwargs)
self.db2 = DbCon()
def register_user(self):
user = self.ids.username_field
pwd = self.ids.pwd_field
rpt_pwd = self.ids.pwd_field_rpt
fname = self.ids.full_name
empnum = self.ids.emp_no
roomnum = self.ids.room_no
info = self.ids.info
uname = user.text
passw = pwd.text
rpassw = rpt_pwd.text
name = fname.text
enum = empnum.text
rnum = roomnum.text
unameokflag = False
passwokflag = False
nameokflag = False
enumokflag = False
rnumokflag = False
info.text = ''
if uname == '':
info.text += '[color=#FF0000]username required[/color]'
else:
unameokflag = True
if passw == '':
info.text += '\n[color=#FF0000]password required[/color]'
if rpassw == '':
info.text += '\n[color=#FF0000]repeat password required[/color]'
if name == '':
info.text += '\n[color=#FF0000]full name required[/color]'
else:
nameokflag = True
if enum == '':
info.text += '\n[color=#FF0000]mobile required[/color]'
elif len(enum) != 10 or enum.isdigit() != True:
info.text += '\n[color=#FF0000]not a valid mobile number[/color]'
else:
enumokflag = True
if rnum == '':
info.text += '\n[color=#FF0000]room number required[/color]'
else:
rnumokflag = True
if passw != '' and rpassw != '' and passw != rpassw:
info.text += '\n[color=#FF0000]passwords do not match[/color]'
else:
passwokflag = True
if unameokflag and passwokflag and nameokflag and enumokflag and rnumokflag:
self.db2.add_row(uname, passw, enum, name, rnum)
info.text += '\n[color=#FF0000]resident details successfully inserted[/color]'
class FoodiesApp(App):
def build(self):
return ScreenManagement()
if __name__=="__main__":
sa = FoodiesApp()
sa.run()

Kindly help me solve the issue.

Let me answer my own question. The problem is resolved. The error "Error type 3 Error: Activity class {org.test.kkfoodies/org.kivy.android.PythonActivity} does not exist." was causing utter confusion. This error was coming because the app was deployed on an android mobile phone where the minimum api requirement is not satisfied. (android.minapi = 21 option in buildozer spec file). Changing the option value to less than 21 also did not help as the buildozer version was not supporting deployment on older APIs.
The app was then tested on android phone which met the minimum api requirement. But the python library mysqldb was causing issues. mysqldb option was added in the requirements attribute and the recipe named mysqldb was tried. But, both the attempts failed.

Finally, the source code file main.py was modified -- mysql.connector library was used in place of MySQLdb. Also mysql_connector option was added in the requirements attribute of buildozer.spec file. That did the trick. The app is working smoothly on android phones now (Android version Lollipop and later). I thank every one of you for the help extended.