Sending an xmpp message, without an xmpp account, to a freedombox user

Is there a way to easily allow someone who does not have any freedombox account and does not have any xmpp account to send an xmpp message to a freedombox user?

Like making a webpage that will allow to write a message and click on a send button, which will send an xmpp message to a predefined freedombox user?

You would need a bridge or interim messaging tool.

i.e
-send send webhook from web page to freedombox homeassistant which can in turn send xmpp message to user.

On my computer, I can use the xmppc command to send a message directly from a terminal.

I could install xmppc and create an html page with a form that will run xmppc (I’d have to learn how to do that), but I was wondering whether there wasn’t something like this already available.

I’d prefer not to install homeassitant for that.

HA was just an example…
Have a look at Apprise…
Should be an alternative that will bridge to what you need