[Help] Persistent 401 Error with SendGrid API in FlutterFlow (Authorization Issue)

I'm facing a persistent 401 Unauthorized error when calling the SendGrid API (/mail/send) from FlutterFlow. The error message is consistently "Permission denied, wrong credentials".

I've already tried the following:

1. API Key: Generated new Full Access SendGrid API keys multiple times. Confirmed the key is fully copied (60-70 characters long after SG.) and pasted correctly into FlutterFlow's Authorization header (Bearer SG.xxx) with exactly one space.

2. Sender Email: My from email address ([email protected]) is verified in SendGrid.

3. Network: Tested on different networks (including hotspot) - same 401 error.

4. FlutterFlow Setup: Confirmed POST method, correct API URL, and Content-Type: application/json header. Body JSON format is correct.

Despite these steps, I consistently get a 401 error. My SendGrid account status is clear.

Could there be any subtle configuration I'm missing in FlutterFlow or SendGrid that would cause this specific "wrong credentials" error, even with a seemingly correct API key?

Any guidance would be greatly appreciated.

Thank you!