Error: Client error: `POST https://login.sellsy.com/oauth2/access-tokens` resulted in a `401 Unauthorized` response:
{"error":"access_denied","error_description":"The resource owner or authorization server denied the request.","hint":"Cu (truncated...)

Response: {"error":"access_denied","error_description":"The resource owner or authorization server denied the request.","hint":"Customer is invalid","message":"The resource owner or authorization server denied the request."}