There's a good reason why you don't want to base a business around unsupported solutions to other companies' problems: those companies can break compatibility at any given moment. And unfortunately, Reserve Strap is discovering this first-hand. The company has stopped shipping its namesake Apple Watch battery band to most customers after learning that WatchOS 2.0.1 and later breaks the strap's charging functionality... you know, its reason for being. Reportedly, Apple doesn't want anyone using the Watch's hidden port (tucked just inside one of the band slots) until there's an MFi accessory program in place.
This doesn't mean that it's game over just yet. Reserve Strap will ship your band if you haven't updated to 2.0.1, and it's pushing for that MFi program to happen sooner than later. Whatever happens, the startup is in limbo unless Apple offers an olive branch and lets this smart strap work for everyone.