Well new one has arrived from Amazon. Same problem, connects but won't pair. Suggests the issue is my end.
iPhone displays a code number that it expects the tablet to show. Which never happens. Attempting to pair willy nilly leads to both iPhone and tablet reporting being connected but the tablet stays stuck on the connection management screen instead of displaying the use CarPlay message to indicate proper pairing.
Did I say how much I hate Bluetooth!
So Amazon is getting the new one back on Monday.
Everything else works just fine on the original one so, as the reverse camera was what I really wanted, I might just wire that in and craft a flip down mount so the tablet doesn't look silly in normal driving. Objectively straight to E-Waste and write off £60 (ish) is a more sensible use of time though.
Unusually for something from China Inc the label had an apparently genuine address, e-mail and phone number for a UK representative. Replab Consulting. Likely fictitious however. Mrs Google finds 4 different addresses for same firm none of which look plausible on Maps. All same phone number but that is dead. E-Mail address actually works and produced a reply saying that they are "only the UK representative, any complaints have to be taken up with the maker in China". Good luck with that methinks. Language in E-Mail text suggests AI generated for a not native English speaker so the whole thing is probably virtual. A for effort but why did they bother.
Clive