403 Forbidden When using WebAPI

I’m trying to use the List Management web API ( BPCC List Management API v2.0 (getpostman.com)).
I get the authentication token without a problem.
But when I try to use it to, say, get a list of Campaigns ( configapi/v2/campaign/getAll/ ) – or any other call for that matter – I get a 403 Forbidden reply code.
Has anyone experienced this?
Or know how to fix it?

I know it’s probably a question of permission, but which one?

One of two solutions (choose any):
Add required privilege to the API user
1). “Manage all services and campaigns”
2) “Manage assigned services and campaigns” and be assigned to the campaign as Administrator, Operator or Reviewer