Full disclosure, I know nothing about Arab-Byzantine coins. It's not a subject I have ever looked at, so the coin below may not indeed be such an example (but I think so). I've looked at many hundreds of examples online and cant find a match, though it may be obscured by the fact it is double struck. 24mm and 6.16 grams. Any suggestions?
Looks like one of the countless overstrikes of the period. Based on the reverse photo the underlying type looking to be a Constans II half-follis from Carthage, like this example from Yale’s art gallery:
