Go to https://console.firebase.google.com.
Click the Add project button.
Fill out the Add a project form and press Create project.
In a few seconds, you’ll see a notification that your new project is ready.
Press Continue to go to your Firebase account.
In the left pane, navigate to Project Overview → Settings → Project settings.
Open the Cloud Messaging tab.
On the Cloud Messaging tab, copy the Server key and the Sender ID.
Paste the Server key and the Sender ID in the corresponding fields in the eSputnik interface.