Why am I not receiving messages on my XMPP account?

Question

linux

Registered on the site www.xmpp.jp, set up the same account in pidgin for Linux, specified the xmpp protocol. I don't remember exactly what I did first: created a pidgin account locally or on this www.xmpp.jp.
In general, I log in normally on the xmpp.jp site, I see my login, let it be user123.
The password is the same as in pidgin for this account.
On another site that requires an xmpp account to register and receive a link to verify the account, my xmpp address was indicated: [email protected] But no messages came.
Maybe pidgin and the xmpp.jp account need to be synchronized somehow? Or am I missing something locally?
Also, when I check the pidgin "create this new account on the server" checkbox in my account settings, it is checked, but when I reopen it, it is no longer checked.
Basically, what am I doing wrong?