In order to enable Cloud Messaging API (legacy) instead of Firebase Cloud Messaging API (HTTP V1), please do the following:
1. Log into your Firebase account.
2. Select a project -> Project Settings -> Cloud Messaging tab.
3. Click on the three-dots (kebab) menu to the left of Cloud Messaging API (Legacy) and choose the “Manage API in Google Cloud Console” option.
4. On the new page, click on the Enable button.
5. Refresh the Cloud Messaging page and a server key will appear.
Feel free to check our official documentation for more information that will help you to integrate QuickBlox services into your applications / projects or contact our Support team by submitting a ticket if you have any other questions.