@johnathon like you see on the capture i am using the login screen.
@llorach-pablo It's been a while since I used .NET Core 5, but are you using a symmetric (HMAC) or asymmetric (RSA, ECC) key to sign your tokens?
The default is HMAC, but for .NET Core, I think you have to use asymmetric keys.
Here's information on creating keys: https://fusionauth.io/docs/v1/tech/core-concepts/key-master
Here's information on setting the signing key: https://fusionauth.io/docs/v1/tech/core-concepts/applications#jwt