For Sumup Air, a portable printer makes sense first and foremost. The following are compatible: Bixolon SPP-R200lliK/BEGE, Bixolon SPP-R210iK/BEGE, Star Micronics SM-L200 (source sumup.ch).
You could also use this printer via a POS system. However, this is a stationary printer that must be connected to the POS system with a network cable (RJ45). Printing directly from Sumup Air to this printer is not possible.

Super well satisfied