UCP doesn’t exist in Asterisk; it’s part of FreePBX. Did you mean to post this to https://community.freepbx.org.
This is not a well formed SIP URI. chan_sip is deprecated, unsupported, and will be removed next year.
The URI part of this is not well formed.
Interesting. It looks like the documentation is incomplete (not surprising), as the possibility of using a peer name isn’t mentioned. However, as the message says, this isn’t a valid peer name and also isn’t a valid domain name, so there is no way of finding the domain name of of the SMS gateway. Message Send sends a SIP message, it does not send a mobile phone message. SIP messages are always sent to SIP URIs, not phone numbers (and Asterisk doesn’t support tel: URIs).
The documentation I am using is: Home - Asterisk Documentation