I purchased the Emon ESP module, and while it worked when I got it, after a few days it was prompting me for username/password. I saw on a post that this is incorrect and I need to reload the software.
I downloaded latest: https://github.com/openenergymonitor/EmonESP
Loaded \EmonESP-master\src\src.ino into Arduino v1.8.9.
Upon compiling, I get:
“Sketch uses 502900 bytes (100%) of program storage space. Maximum is 499696 bytes.”
Edit: Solved. I had to change Flash Size: 4M (3M SPIFFS). By default it was 512K No Spiffs. That did the trick!