okay, got it. The issue is, that you have authenticated with a Gmail account (abricool@abricool.ch) which you are using in the receiver's email. This won't work. The authenticated account and sender should be same.
You need to use the sender's email with which you have authenticated or it's should be an alias.
For now, if it works with your usecase, you'll require to build an API key version of the it, and then your user's can upload their own keys via FlutterFlow - https://docs.buildship.com/tutorials/byok using BYOK.
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