Follow below mentioned steps to create Firebase JSON file :
Step 1 : Go to Firebase and Sign in to your account.
Step 2 : Click on Get Started
Step 3 : Click on Create a Project
Step 4 : Select your Project name to add Firebase to your already created Google Cloud project, then accept the Firebase terms and click on Continue.
Step 5 : Click on Continue.
Step 6 : Enable Google Analytics for this project if disabled, and click on Continue.
Step 7 : Select the Country, accept the Google Analytics term, and click on Add Firebase
Step 8 : Wait till the project gets created and once your project is ready, click on Continue.
Step 9 : Click on the Android icon.
Step 10 : Add Firebase to your android app by providing the required details:
Step 11 : Once you have provided the required details, click on Register app.
Step 12 : Download the google-services.json file on your system and Click on Next
Step 13 : For the Add Firebase SDK step, click on Next.
Step 14 : Now, click on Continue to Console.
Step 15 : You will be redirected to your console dashboard. Click on the cogwheel icon next to Project Overview.
Step 16 : Select Project Settings.
Step 17 : Under Public Settings, select the Support email from the dropdown menu.
Note: Your support email will be the email address presented to users when they are authenticating with Google.
Step 18: Now, go to Appy Pie’s Login/Signup section in System pages.Upload the downloaded JSON File in the respective box.