Firebase Cloud Messaging: REST API responds with "INVALID_KEY"

Question

Our push notifications work fine with the in-built tester on the firebase console website.

However when we try to use Postman to simulate a push request to fire off "our own" notification the server always returns "INVALID_KEY" Error 401.

Where is the correct Key located? So far we tested:

• Web Push public key (green are in the following image)
• Web Push private key (located in the options menu in near the green area in the image)

When using these keys in Postman (plus the required body) the previosly mentioned error is returned:

What are we doing wrong? Do we need a completely different key? Thanks in advance!

Answer 1

Found the solution: you have to create a Legacy Setup of the Cloud Messaging API under Project Settings > Cloud Messaging.

To do so press the three dots next to "Cloud Messaging API (Legacy)" and enable the service. It then automatically sets up the environment and present the key.