Limit input length
Zulip's Nginx returns "414 Request-URI Too Large" when the input is too large, because it requires the message to be sent as URI params. I've done tests with JSON body and form encoded but it didn't work, it returns an error saying it can't find required fields.
The JS library suggests form encoded should work: https://github.com/zulip/zulip-js/blob/main/src/api.js#L11