Starting 1.18 theme version you can add new custom fields from General-Custom Fields

We support as custom fields: dropdown, text fields, number fields, date fields. They can be ordered from theme options. They will always show after default fields.

This is the submit form and where custom fields show in submit, AFTER default fields in DETAILS settings:


This is the property front page. Custom fields show under Listing Details, after default fields:

custom fields