Invalid_Client with Flask and AuthLib

I'm running the Flask Authlib OAuth 2.0 exemple from github: OAuth 2.0 Provider

Everything seems to be working.

I can create clients and all.

But, I can't do a Password Grant.

Every time I do a Password grant it just returns:

{"error": "invalid_client"}

Or it returns:

UnicodeDecodeError: 'utf-8' codec can't decode byte 0x9e in position 0: invalid start byte

Don't know what is happening. I'm using Postman to do the post requests. But, on terminal using the following command:

curl -K user -X POST -d "grant_type=password&email=email&password=password@&scope=read" https://localhost:8585/oauth/token