On 20/01/2021 15:37, Charlie Pridham wrote:

NB we dont have a mobile phone signal worth the name on any network or I
could use that as the tablet has a sim card

There is another possibility but it is more fiddly that the other one I
suggested which is OK for the relatively low bandwidth you would need
for a credit card machine.

Hauwei Mifi pebble with and external antenna capability
Yagi antenna for appropriate waveband on your nearest mast
Interconnect cable
Three 200MB/month for free SIM (or a 12 month EE/Three data SIM)

I have worked masts up to 25 miles away with that setup. It is fiddly to
get going the first time. You really need the antenna on a tripod with a
pan tilt head to do fine adjustments. The high gain and directionality
come at a price but you can turn no signal into a 20MB link or better.

--
Regards,
Martin Brown