Just to be clear, your username is not case sensitive. In this case, your callsign on your profile was lower case. Many (most?) people have usernames that have nothing to do with their callsigns, and the callsign is saved as a separate attribute on your SSO account.
True. I had web apps in mind when I said that.
But the SOTA Spotter app specifically asks for the SOTAWatch Username, which isn’t case sensitive via a web browser (I’ve logged in both ways).
That said, I looked at my account settings and the username (in this case my callsign) is displayed in all caps, so while the web browser access method may not care, it appears the API does. Knowing that now “fixes” the problem for me. 
No, you log in with your username. That process sends back a nice little packet that includes a bunch of information, including for example your Callsign from your profile, your Latitude, Longitude, name, etc.
Your callsign on your profile was lower case. That’s all I changed. When you logged in and out on SOTA Spotter, that sent a new packet with a new profile information.
[quote=VK3ARR] No, you log in with your username. That process sends back a nice little packet that includes a bunch of information, including for example your Callsign from your profile, your Latitude, Longitude, name, etc.
Your callsign on your profile was lower case. That’s all I changed. When you logged in and out on SOTA Spotter, that sent a new packet with a new profile information.[/quote]
Gotcha. I misinterpreted your earlier comment about logging out and back in and thought when you said my callsign was lowercase that it was an issue with what I was typing into the app, not something on the server side.
Thanks for your help. 
I’ve seen this issue. I have for completely exit the program (swipe up when it shows all the apps running) and restart. It will then allow me to edit. This workaround had never failed.