Apps besides iZettle and SumUp : No, unfortunately the development is tailor made for those two apps.
But if you need anything specific for some given app(s), it might not be very heavy to adapt current code base. The most difficult part is to achieve to retrieve data. Here I hacked the system by using iZettle and SumUp APIs (i.e. my application does not communicate with iZettle and SumUp applications on your device but rather through the public APIs of these shops).
Do not hesitate to contact me if interested.","title":null,"type":"comment","url":null}],"created_at":"2020-07-20T19:41:37.000Z","created_at_i":1595274097,"id":23901163,"options":[],"parent_id":23900747,"points":null,"story_id":23900747,"text":"Could you use this with thermal transfer shipping labels and apps besides iZettle and SumUp?","title":null,"type":"comment","url":null}],"created_at":"2020-07-20T18:53:19.000Z","created_at_i":1595271199,"id":23900747,"options":[],"parent_id":null,"points":2,"story_id":23900747,"text":null,"title":"Show HN: Low-cost receipt printers for iZettle and SumUp","type":"story","url":"https://www.ploumpouloum.com/en/receipt-printer"}