@Juzau, hm, that’s odd. Did you definitely use the postcode which is on your DS’s GP records? Eg if you’ve moved house since you registered with the GP and didn’t update them as to your new address, then the system won’t recognise your GP. And did you use the exact name which is on his GP record? Eg if you put “Stan Smith” but the GP record has “Stanley Smith”, or if he’s officially Stanley George Smith (on her GP record) but you always call him
George and you entered that on the vaccine booking website, then it won’t recognise that either.