Don’t use Asterisk 18; it is two months into its security fixes only, final, year.
I hope you haven’t quoted your real password!
Generally, to debug something like this, you need to enable the full log and turn on protocol logging, using the CLI. For chan_sip, that is “sip set debug on”, for the chan_pjsip, that you should be using, it is “pjsip set logger on”.
You definitely should not be using this any more - chan_sip is unsupported,
deprecated in the version you have, and no longer included in current versions
of Asterisk.
Please start with a currently-fully-supported version of Asterisk, and a
supported SIP channel driver (PJSIP) so that we can give better advice on any
problems you run into (many people here no longer have recollection or
familiarity with using chan_sip).