Linguistically, a commission isn’t primarily an offer of payment, and commissions aren’t always remunerated. Consider this definition:
1.1 (with object and infinitive) Order or authorize (a person or organization) to do or produce something.
‘No one commissioned him to preach; and he belonged to no church.’
The main thing communicated is the order and authorisation. Payment might be expected, as might housing, and both might accompany the commission, but the commission itself is simply the order and authorisation.
In the context of art, warfare or commerce, however, payment would be expected when someone is commissioned to do something. However, one can be commissioned to an unpaid role. Here are some examples:
Those commissioned as unpaid special Rangers under the new law would “act as a secret service department for the State"
- Time of the Rangers by Mike Cox
The justices of peace were commissioned as unpaid local officials for Henry the 7th in England
- The New Monarchs
The expectation of payment might come from the reasonable notion that if one wishes someone else to accomplish some work, someone needs to furnish what is required for the work to take place. It would be typically be unreasonable to assume that the worker would work for free or to pay for the raw material. However, expecting payment in the typical case isn’t the same as requiring it in every case.