Why am I getting an error « HTTP 414 Request-URI Too Long »?

The URLs that Matomo Mobile requests are usually not longer than 500 characters and should not cause any troubles. In the past we noticed some troubles if a WordPress plugin like « iThemes Security » was used though. It should work if you disable this plugin. Or you could try to go to iTheme Security options > System Tweaks > and just disable « Filter long URLS » option.

In case you are not using plugins like iTheme Security you might want to have a look at LimitRequestFieldSize and LimitRequestLine for Apache or large_client_header_buffers for Nginx.