The User Choice Contract Number should be entered in the AVETMISS section of the Course details window as per image below. The Contract Schedule should be entered as well:

Note: This contract number will apply to all Clients (Students) in that Course.

Along with the contract number you might need to record the Registration Number (which is sourced from a DetConnect spreadsheet, if using DetConnect). The Registration number is to be recorded in the Enrolment>AVETMISS>Training Contract Identifier field: