I am a new Verizon FIOS customer and I am not yet able to authenticate on WatchESPN. How much time would it takes for my credentials to be propageted to WatchESPN service?
Are you a brand new FiOS subscriber who just went through the installation process, or did you perhaps just add FiOS TV to an existing Verizon set of services?
AFAICT the answer is forever. It's never worked for me with any web browser/OS combination. Verizon technical support has been exactly as helpful as you would expect.
Not to rehash it, but are you using the same email address as the primary account?
I have been a FioS subscriber for many years and was able to log into WatchESPN on my laptop until recently. Now I get the same authentication error every time. Username and password are correct and the app works fine on my phone.