Hi Andrew - in light of the fact that your pistol is a Model 1922, and than Serbia ceased to exist as a separate country in 1918, when it became a part of the Kingdom of Croats, Serbs and Slovenes, it would be more proper to call it a contract for Yugoslavia, the name given to that amalgamation of countries.
Your pistol should have a crest on the front end of the tubular slide, which is the Kingdom’s crest, and is sometimes referred to as King Peter’s Crest. On the left side of the slide, there would be a word or combination of words, defining which service it was made for. I believe there are five different markings found, three of which, at least, are in the Cyrillic form. At one time, I have one marked (practical translation) “Army Property” and one mark simply “Police.” These were in Cyrillic. There is one marked specifically for the Police of the city of Split, and one for the City of Zagreb. I can’t reproduce Cyrillic here, and unfortunately, have no translation for the fifth one. The one markd as “Army Property” is the most common. I can reproduce the first word of that two word marking, as the letters have the same form as those of the Latin Alphabet, although perhaps not the same sound - “BOJHO.” Unfortunately, Balkans languages are a mystery to me.
The correct cartridges for these pistols, depending on when the ammunition was made for them, would have headstamps like the following, which are in my collection
F O M U 34 (also known with 35 and 40 dates)(the letters are in the Cyrillic Form)
IK 03 9X17
- 11 * 55
nny 61 (The Cyrillic equivalent of “PPU”)
PPU-64 CAL.9-K (alsoknown with 66 date and “CAL.” abbreviation)
PPU-67 KAL. 9-K (not spelling of “KAL.”)
CAL.9mm PP-72 (also known with 74 date)
9 - K nny-82 (also with 83 date)
nny-88 .380 AUTO (this is likely a commercial headstamp due to “inch” caliber designation).
There are later commercial headstamps by PPU (Prvi Partizan Udice) but they are quite modern and purely commercial.
Hope this is of some assistance.