exchange id porten access token to altinn token. `exchange/{tokenProvider}`

### Description of the bug

TypeError: Failed to fetch
Code: undocumented

### Steps To Reproduce

1. https://docs.altinn.studio/nb/api/authentication/spec/#/Authentication/get_exchange__tokenProvider_
2. Execute with access token from id portelen with test=true

### Additional Information

_No response_

Open the linked Authentication/get_exchange__tokenProvider_ endpoint documentation and reproduce the failure using an access token from id porten with test=true. Trace the reported "Failed to fetch" result and confirm the endpoint behavior or documentation issue that needs correction.

Written by the indexing model from the issue text.