Follow below mention steps to get your Firebase (Data) url:
1: Open firebase Console and login using your gmail account credentials.
2: Provide a name to your Project and click on Create Project button.
3: Select Database from the side panel there you will find your firebase url under Data tab.
4: Copy your Firebase url from Data tab of Database section
5: Replace code with the following code (same as shown in below image, if its not same already) and click on "Publish" button.