Futaba FHSS receiver issue

[Hog]

Recently purchased a Futaba R204GF-E receiver from a well known auction site to be used in one of my cars.

For some reason however I cannot get it to bind with my T4GRS. I've followed the procedure and just get a flashing led on the receiver which apparently means "mismatched ID" whatever that is.

I've tried binding on FHSS, S-FHSS and T-FHSS modes but without success.

The seller has been very good and has offered a refund but I thought I'd ask on here before I return it if anyone else has encountered such an issue and whether they managed to resolve it, or what the "mismatched ID" means?

TIA.