Explanation: Roman soldiers were paid according to a set scale - with centurions making 16 times that of the common enlisted man - including 16 times the retirement bonus. Quite a pretty penny! Auxiliaries, non-citizen troops, got even less than enlisted legionaries - but oftentimes, in other contemporary militaries, pay was unreliable or nonexistent. At least knowing you have a paycheck is something!
I thought Auxilia got supplies on mission from Rome, but we paid by their home provinces. Maybe this is a time varying thing.
There's a lot of variance over time, but you might be thinking of foederati, who were troops provided by allied 'barbarian' polities, supplied by Rome (because what use are starving troops?) but otherwise kept under their own military traditions. How much auxiliary pay was is a surprisingly contentious topic in academia, but it's generally accepted that they were paid, and paid less than legionaries (I used the 2/3s estimate).
The home provinces of most auxiliaries would not have had the institutional capacity to get money from Point A to Point B on the other side of the Empire - provinces had surprisingly ad hoc organization, in contrast to local cities and the Empire itself.
