Aside from the QR code not being scanned as required , have you not been paid at all  OR are you funds on hold since eBay see you as a 'new' seller?

Plus, the buyer is yet to leave feedback

So thus far, you have no proof they have been picked up/supplied

Have you tried 'marking as sent'

Were the items originally listed with a pick up option, or did the buyer ask you if they could pick them up instead of posting them?

Not everyone has the ability to scan the codes - do they have a numeric number which can be entered.

If so ask the buyer to supply same.