firebase push notifications by API call failed, error code400 and "The registration token is not a valid FCM registration token"

Database & APIs

my flutterFlow setting, custom backend without auth using firebase, have enabled push notifications connecting with firebase. use custom code to get FCM token successfully. I try many way to generate access token(gcloud, node), still not working,please guide me how to fixed it, thank you so much everyone.

POST return 400 error message: "The registration token is not a valid FCM registration token", "status": "INVALID_ARGUMENT"

https://fcm.googleapis.com/v1/projects/my_project_id/messages:send

Headers: "Authorization": "Bearer $accesstoken

Body: {

{

"message": {

"token": "FCMtoken",

"notification": {

"title": "acb",

"body": "FF hello"

}

}

}

What have you tried so far?

or any suggestion I should use one signal with custom backend will easy? thank you

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