The app/UI limits the url to 50 characters, yours is more than 50 characters. There has to be a limit because the controller does not have infinite space to story the MQTT configurations (it only has about 300 bytes to store the entire MQTT configuration). Last time we had to increase the limit, it was because someone’s MQTT account has a password that’s 100 characters long. Then it was because someone has a user name more than 50 characters. We can certainly increase the limit a bit, but I won’t be surprised next time someone would have a MQTT server url that’s more than 200 characters long…
In the meantime you can always send in your MQTT configuration via HTTP API, to bypass the limit set by the UI. The code is in options.js, search “Broker/Server”, then maxlength in the id='server' field.