If you want to play in network (netplay) on Recalbox with your Roms, it is necessary to have the CRC32 in the gamelist.xml of your Roms.
Here is the method to add the CRC32 in the gamelist.xml file:
ARRM will review all the Roms and calculate the CRC32 of each of the Roms files, then fill in the 'hash' Tag which will be added/updated in the gamelist.xml when it is saved.