Hi Jonathon,
Thanks for your help, it looks like what you have highlighted is the problem here.
I tried logging into DDM Reporting UI and I couldn't see this user profile listed there, although I could see it in DCM UI.
Also, I tried calling the methods for which only trafficking scope is required (ads.list, campaigns.list), and they are working fine. But all the methods for which Reporting scope is required returns 'invalid profileId' error.
I have confirmed that the user role associated with this user profile has "DFA Reporting access" permission. What other permission are required for Reporting access? And is that on account level or user profile level?
Thanks,
Akshay