MyBB Community Forums

I am using Volare Responsive theme and when viewing posts, at the very top, this error shows up: 

The following warnings occurred:
Warning [2] Use of undefined constant username - assumed 'username' (this will throw an Error in a future version of PHP) - Line: 50 - File: showthread.php(1600) : eval()'d code PHP 7.4.16 (Linux)

File
Line
Function/showthread.php(1600) : eval()'d code
50
errorHandler->error
/showthread.php
1600
eval

I had the same and fixed it here: https://community.mybb.com/thread-232677.html