We just get our Squareup POS Integration on the Linnworks Application Store. You can install the application directly from the store, just search for Squareup:
In our pipeline is a release of the Sumup POS integration as well, please let us know if you would like to participate in BETA.
We are open to the suggestion for the next POS integration!
If you have any questions, please contact us via firstname.lastname@example.org