No required module provides package after running go get

So I have a GOPATH set to my working directory and I create a new script file.go. In that script I use I import "github.com/..." I ran 'go get github.com/... and it appeared to download but when running go run file.go I still get: no required module provides package github.com/gordonklaus/portaudio: go.mod file not found in current directory or any parent directory; see 'go help modules'.

I tried adding go.mod but then the error just changes to:

go: no module declaration in go.mod. To specify the module path:
        go mod edit -module=example.com/mod

So I adding the following to my go.mod file and it looks like this now:

module MyModuleName

go 1.17

require(
	"github.com/..." v1.2.3
)

But I get:

missing go.sum entry for module providing package github.com/...; to add:
        go mod download github.com/...

But when I run go mod download github.com/... I get:

github.com/...@v1.2.3: invalid version: unknown revision v1.2.3

So I don't know what todo from here.

I would:

• edit go.mod and remove the line where v1.2.3 is
• go get github.com/gordonklaus/portaudi (executed in the project folder, where go.mod is)
• go mod tidy

The end result should be the library added with a tag matching its latest release.

If someone having similar error:

go: no module declaration in go.mod. To specify the module path:
        go mod edit -module=example.com/mod

while trying to run some go code like go run test.go, the following helped me to eliminate the error:

GO111MODULE=on go run test.go 

After that I was able to run go code normally, without specifying GO111MODULE variable.