How to send a form from an html page to a page that is generated by a binary code?

Question

XMPP

there is a form on the server ( https://omemo.ca:5281/register-on-omemo.ca) it cannot be edited externally, it also has a captcha, which is not desirable to remove. on another site I made a beautiful form https://monolith.plus/xmpp/xmpp-register.html
I duplicated the name for the fields (the same as on the registration site), but when submitting the form, it redirects to the register-on-omemo.ca page
I also want note, I took the entire form in iframe, along with captcha, in this case everything works fine, but the unedited appearance also remains, so this is not suitable.
I suspect that it redirects to the page due to captcha on omemo.ca