Guest Does not See the "Pay Now" Botton on Payment Requests

    We are new to Reservation Manager.  I have had two guests this spring that received the Payment Requests but they did not have the "Pay Now" button.  We go round and around trying different web browsers and different settings.  One guest gave up and mailed me a check and the other guest finally got "Pay Now" to work using a different computer.  Is there a standard set of instructions we can provide guests that are not computer expertson using Reservation Manager?  Is this a browser or privacy/security issue?  Suggestions?