Can anybody identify this wall plate potter please?

I think it's made out of terracotta?

The makers mark is towards the centre of the back of the plate to the side of the string. I've drawn the makers mark on photo 3

Not one I recognise. Is the X part of the mark inset or raised?

It's inset

Robert Mabon has a similar stamp. The raised parts of his stamp, between an inset cross, are triangular shaped but your drawing doesn’t look like they are on the mystery mark

Thanks Naomi looked at Robert mabon also Robert Brady but not the same.