SMS is send directly from reservation part.
To be able to send a message, guest reservation details, in this case phone number muss be added in reservation details.
As well myRent user details, in this case phone number must be added.
To send a message to to the one reservation and under contact details, find phone number. On the right side of the phone number you will find a button with: CONTACT VIA SMS.
When the message was sent you can find in the Infobip Logs (Settings-B2B connections)-Infobip.
As well you can find it your Infobip account: