I now switched to another account for which I'm pretty sure it's not a trial:
"subscription_type": "PERSON_PREMIUM_V1",
"subscription_type_downgrade": "PERSON_TRAVEL_V1",
"status": "ACTIVE",
"sub_status": "NONE"
But I'm getting the same error.
By the way, for either account if I do a GET monetary-account in POSTMAN it will return a 'Insufficient authentication' error.