Originally Posted by
gaggia
.... MP is refusing to credit me miles for this connection, ....
United is not posting because Avianca is not approving the posting. The decision is in Avianca's hands. Numerous *A carriers are not supporting mileage earning of their low-cost subsidiaries.
Aviateca / Avianca Guatemala is listed on Wikipedia as Star Alliance (affiliate) which has not guaranteed miles in other cases. In the *A system the flight operator makes the decision on mileage earning.