The manual at https://wiki.mikrotik.com/wiki/Manual:Tools/Sms#USSD_messages shows how to send a USSD message, and this works:
/tool/sms/send lte1 phone-number=“1361#” type=ussd
I get a response inviting me to continue the conversation by sending “1”.
How do I sent the “1” using the /tool/sms/send tool? Docs don’t confirm this.