Hi @erezst,
Welcome to the Auth0 Community and sorry for the late reply!
Most likely in this scenario you are not passing the audience claim to your request. That is basically the indented consumer of the token, typically the resource server. For that reason you might be getting an opaque token, so i would recommend checking out our Validate Access Tokens Documentation.
You can specify the audience in your request as described below:
"aud": "https://test-api"",
More information about this can be checked under this Knowledge Article.
I hope this helped,
Remus