I wish to really thank Ryan from 360Works for being so incredibly helpful with this problem. The problem I experienced was not due to anything wrong with the Email Plugin. The problem solely occurred at Amazon. Through multiple emails with Ryan, and spending wayyyyy too time reading through Amazon's murky documentation, I was able to restore functionality of sending SMS messages. I never received any error messages from their (Amazon) site, but I could tell that messages were reaching their servers. I can't tell you exactly what was the exact trick that worked, but as suggested by Ryan, I increased the spending limit budget and changed the style of message from "promotional" to "transactional". I made other modifications, but I feel that the main changes solved the issue. Ryan sent me link from other Amazon clients that had had similar problems. I'm not impressed with their attention to support. I have 36 years of IT industry experience, but their user interface totally lacks easy comprehension. Again, I want to thank Ryan and everyone at 360Works for superior customer service.
Per 360Works documentation for sending SMS Messages using their plugin, I created an Amazon SES Account and IAM User. I created the Access Keys used by the plugin, and I was successful sending SMS Messages for about 10 days. Abruptly, the ability to send SMS has stopped, and I do not receive any errors in my scriptstep "EmailSMSSend" using the FM Debugger. It appears that FileMaker is able to hand off the message to Amazon, and it dies there. I have tried creating other IAM Users (although the plugin only requires the Access Keys). I have created new Access Keys, with the same failure. Using the Amazon Management Console, I cannot see any errors that I can correct (I find their Console and UI incredibly daunting). The Console talks about Topics and Subscriptions, but I don't understand how that applies to my need. Does anyone have any insight to my plight, and where I can resolve the issue?