Custom fields from /rest/api/3/fields with Oauth

Hello @harry88

  1. What type of ‘app’ are you creating?
  2. What development language / framework / libraries does this app use?
  3. Which specific API endpoint are you accessing to get those custom fields (I don’t know of any endpoints that end with the word ‘fields’)
  4. What is the actual request being sent to that endpoint with what parameters?
  5. What are the scopes being using with that request to that endpoint?
  6. What documentation are you referencing and what tests have you done outside your code using your API test tool?

Refer to the How to ask a good question thread on the minimum amount of information that would be required to be able to assist with your problem.