1) You should contact Guest Link support so they can provide you a "unique reference" for your units - (0844 209 2555). There may be charges for calling so please check on their site beforehand so you are aware of any fees.
NOW GO TO YOUR PROP-SYNC ACCOUNT
1) Once logged into prop-Sync, go to "settings" in the top tool bar, then scroll down and select the unit you wish to link the calendar with and choose “Guest Link”.
2) In the box it will request a reference which you should have retrieved from Guest Link support. Insert the code here, e.g. 998D1353 and "register" to synchronise.
Your calendars should now be synchronised, if you're worried that they're not you can contact Prop Sync to check this for you or call so they can support you through this process.