SIM900 module activate roaming

I have the following problem:

I've connected a SIM900 module to my Arduino board. The sim card seems to be working because I can call the number. (and I see the approriate lights flashing when I do the call on the board)

The issue is that I cannot use the GPRS. I have a German SIM Card and currently am in France, therefore my best guess is that I have to activate the roaming option somehow. (Especially since the GPRS worked in Germany)

I am using this library: GitHub - MarcoMartines/GSM-GPRS-GPS-Shield: GSM/GPRS & GPS Shield Library for modules using SIM900/SIM908

Of course I can just buy a French Sim card, but just out of curiosity it would interesting to know how to activate roaming.
Does anyone have a clue?

(and attached a log from the GPRS example of the library )

Thank you guys!