Open Android Studio
Open project folder and go to the Terminal. Copy the below command and paste it and hit enter.
For Mac
keytool -list -v -keystore ~/.android/debug.keystore -alias androiddebugkey -storepass android -keypass android
For Windows
keytool -list -v -keystore "\.android\debug.keystore" -alias androiddebugkey -storepass android -keypass android
Note : If you still can't find SHA-1 key, Please follow the Link and complete the setup as asked.
This way you can get SHA-1 key