Tyre sensors not detected error

[snowie]

Looking for some advice please.
Getting the error “Tyre sensors not detected” on my 2017 Custom, which has had original wheels replaced with 18" alloys.

3 weeks ago, had ABS sensor problem, which produced 'Park Pilot malfunction', 'Hill Start assist not available' and 'Tyre Monitor not detected' errors, with ABS and Traction Control warning lights coming on.
ABS sensor was then replaced and was advised at the time that the ABS sensor detects tyre pressure 'drops', and therefore no sensor in tyre/wheel.
Information system on the van only alerts to tyre pressure drop and does not indicate which specific tyre or the actual pressure on each wheel, so thinking perhaps sensors in the wheels are not required (?)
The day after ABS sensor was replaced, cracked a rim on one of the alloy wheels causing slow puncture. This has now been welded and is okay, but the 'Tyre sensors not detected' error is coming on.
The company who did the weld says there are no sensors in the wheels, tyre pressures monitored by ABS sensor.

So, do the tyres/wheels have a physical sensor inside them? Or is tyre pressure monitored through the ABS sensor.

Any advice greatly appreciated. Thanks

[snowie]

I should have added that if I reset the 'tyre sensors not detected' error through the 'settings', the error will clear, but comes on again after driving 6 or 7 miles.