Can anyone please tell me what should be in this rectangular hole just below the door pocket, and the matching one in the other door?

They are where puddle lights go. You can easily buy replacements on line such as eBay and Ali express for about £8 a pair. You can get light projected designs too . The wiring is probably in the hole and the units are often plug and play

I have reflectors not lights

Try these from eBay, item no. 276103029649

The genuine ones can be found on Amayama:

Or you can look around for part number 81911-28010.

Getting one locally will save waiting for a couple of weeks.

I hope this helps.

Paul

Many thanks everyone