... you must already have a debit card stored and which has been used, on your Google Pay. And crucially, you have to use the Google Chrome browser to do this. ...
What's your source for this? It would explain why I have to use the bar code rather than NFC, as I've never used Google Pay to make an NFC payment. (My NFC is on and working fine for other things )
Also just seen the Club's latest guide for Android users like me, which says:
"Alternatively, you can click ‘show code’ to display a barcode and the (sic) hold your smartphone
on the reader."
That's not right. If using the barcode, it has to be held so that the barcode is visible to the scanner. That means inserting it face up into the slot. If the barcode is nearer the bottom of the screen than top, and you have a particularly long Android phone, it might need to be inserted bottom first. Turning screen brightness to max, not automatic, can help.
If you have a very thick phone, it might not fit in the slot, so you better hope NFC works.