Information on WWI Prisoner of War 50 Pfennige

Can anyone help to identify the reference number of this banknote and the meaning of IX.A.K
Any other information, as o where it was used would also be very helpful.
Have been looking at the Banknote Museum website, but cannot find it listed there.

It measures 55mm x 39.5mm and is made of cardboard about 3/4mm thick

https://en.wikipedia.org/wiki/IX_Corps_(German_Empire)

IX. A.K. refers to IX (9th) Armee-Korps.

Other than that, the compound word on the obverse, "Kriegsgefangenenlagergeld" means prisoner-of-war camp money.

I have found a note like yours here (Lot No. 630), which says it is from Güstrow POW camp:
https://qs-sincona.auex.de/Auktion/KatalogArchiv?intAuktionsId=208&los=1024656

https://navonanumis.blogspot.se/2017/03/bereich-des-ix-armee-korps-altona.html?view=magazine
Bereich des IX Armee Korps, Altona: German Empire POW Camp during the Great War
"The IX Army Corps was based in Altona, Germany and had jurisdiction over Furstenberg, Gustrow, Lubeck, Neumunster, Parchim, Bremen and Hamburg.

The 50 pfennig notes (C-2620) were issued in Bad Stuer, Furstenberg."


https://picclick.de/Kriegsgefangenenlagergeld-1917-50-Pfennige-IXAK-Top-Erhaltung-253348919216.html