Can't get nested key from env to override yaml config file using viper

This is my simplified config:

stripe:
  secret_key: sk_fromconfig

Why viper don't take value from env?

% echo $STRIPE_SECRET_KEY
sk_fromenv
% go run main.go 
sk_fromconfig

I expect it takes value from env because I have one like this:

% echo $STRIPE_SECRET_KEY
sk_fromenv
% go run main.go 
sk_fromenv

Here is the code:

package main

import (
	"fmt"

	viper "github.com/spf13/viper"
)

type Config struct {
	Stripe Stripe
}

type Stripe struct {
	SecretKey string `mapstructure:"secret_key"`
}

func main() {
	viper.SetConfigName("config")
	viper.SetConfigType("yaml")
	viper.AddConfigPath(".")

	viper.AutomaticEnv()
	_ = viper.ReadInConfig()

	var config Config
	_ = viper.Unmarshal(&config)

	fmt.Println(config.Stripe.SecretKey)
}

I tried viper.BindEnv("STRIPE_SECRET_KEY") and viper.SetEnvPrefix("STRIPE") but didn't work.

Use viper.SetEnvKeyReplacer, because it wasn't automatically replaced from . to _

viper.SetEnvKeyReplacer(strings.NewReplacer(`.`,`_`))

so it was looking for environment variable STRIPE.SECRET_KEY but since most shell doesn't allow dot in the environment variable name, we have to replace it with underscore.