Hi @tomg12345, welcome to the community!
I can see that the Support team got back to you with this reply:
I was able to look in our logs and I am seeing a 400 error "Invalid grant". Have you tried creating a brand new Firebase connection within the Zap? If not, I'd recommend giving that a try.
I also did some research and found that generating a new SDK key may help as well. Once that is done, try reconnecting the account once more.
Additionally, reaching out to Firebase/Firestore may help as well, as their support team may be able to take a closer look at your account to see if any setting need to be updated
If you’ve tried the suggestions above and it didn’t help I’d recommend going back to the Zapier Support team, explaining the steps you’ve taken and they can take another look to see if we’re still getting the same error message in the Zap logs.