Answer:  

At this time, some PMS systems (such as Loventis and Wix) only support one property per username.  This is a limitation of the PMS.  

Workaround:  

1. Create the 2nd property in myallocator.  Here is how:  How to add, manage, and remove multiple properties in your myallocator account
2. Go to Manage, then Users.  Add another User account that has permissions only to your second property.  Here is how:  How to add and manage myallocator users
3. Login to your PMS and enter that new Username and Password combination that you created for the second property.  This step can be performed multiple times for multiple properties.