WiFiManager - Combine NonBlocking portal AND addParameter
The WiFiManger's autoConnect function starts the configuration web server (and AP) only if connection to configured WiFi network is not established.
If you want to run the WiFiManger's web server to reconfigure WiFi or to set other parameters, you can start the WM web server with the startConfigPortal function.
autoConnect and startConfigPortal are blocking by default. The library has a loop inside this functions which runs until the web server is stopped calling [Exit] action on the configuration web page or the timeout set with setConfigPortalTimeout is reached after last contact from browser.
To run the WM web server 'parallel' to your sketch you can configure it as not blocking with setConfigPortalBlocking(false). Then to allow WM handling of the web server the sketch must periodically call wm.process().
In not blocking mode the [Exit] action on the configuration wen page doesn't stop the web server. The server must be stopped in code.
The parameter definitions must by global in sketch, if you want to run WiFiManager with parameters outside of setup(). Parameters local in setup() don't exist after setup() finishes. WiFiManager detects this and doesn't use the parameters.
The OnDemandWebPortal example and OnDemandNonBlocking example demonstrate startConfigPortal in blocking and not blocking use.