Purchased one I’d say three years ago and S8 will charge fine but not ip8 at all. Does something need to be unabled on the iPhone? Maybe charging pad is too old? It is a Duracell Powermat.
I have a Nokia DT900 and whilst I have a chunky case on my Microsoft phone and can drop it on there without careful placement I’ve noticed the 8+ needs putting down at the right point otherwise it’s repeatedly trying to charge then not charge. The 8+ also has a case, I’ve not tried it without. That said now I know how to place it, it’s no big deal and might get another one if I can find them cheap enough! (This one only cost me £6 in a clearance sale new about 18 months ago)