Thanks for comments. rragan you are correct that 5c does not go up to iOS 11 i'm at the highest version possible with 10.3.3. However on checking the Apple Store no where does it mention you have to have Apple Watch 4. If this is the case it is a straight mis-selling of the App as all it says is Apple Watch app available.
Will be demanding a refund.
Also cachly needs to update the requirements section to say Version 4 of the watch is required and that to use the Apple Watch iOS 11 is needed
Oh and Reagan. The App does not show anywhere in the Apple Watch menu. Probably because not version 4.
Well all this was a waste of time. Cachly being deleted and back to the geocaching, com app as without working on my watch it is pointless as the original app does the same.