Access Token is not valid and is truncated

We are facing an issue with the authentication of the user and receiving a valid access token for usage in API.
Here is the authorization request that we use:

final AuthorizationTokenResponse? result =
await appAuth.authorizeAndExchangeCode(AuthorizationTokenRequest(
'cbGHti4Cgf8SbDVmucnfkgbSorLSCfmZ', 'com.example.AnoGeo://',
issuer: '',
scopes: ['openid', 'profile', 'offline_access'],
additionalParameters: {
'audience': 'anogeo-api',

After the successful beginning we receive AuthorizationTokenResponse with the next access token:


which is not valid if to check in or our API.

Where can be an issue and how to receive the correct access token to work with our API?