Marketo Auth Error

Overview - Receiving a successful response from the Marketo API however, the response body returns a 603 error code with Access Denied.

Cause - The above 603 error is returned from Marketo when the authentication has been successful but the user doesn’t have sufficient permission to call this API. 

Resolution - This can be resolved by logging into Marketo and following the steps below.

1. Go to Admin > Users and Roles
2. Select API User and identify what role it is assigned to (e.g. API role)
3. Go to Roles and check the permissions assigned to the API role
4. Check to see if the API role does not have 'Read-Only Activity' or 'Read-Write Activity' permission

Further information can be found in Marketo's public documentation here.