You have received a message like this one and are wondering what to do to resolve this:
From: ORG's Admin Name <firstname.lastname@example.org>
Date: Friday, 26 April 2019 at 08:40
To: Peter Parker <email@example.com>
Subject: Propertybase system notification: Duplicate field detected - admin intervention required
Hello Peter Parker,
We have detected a duplicate field in your Propertybase account located on the pba__Listing__c object, with the field name of Property__c.
Please rename or remove this field as soon as possible.
When duplicate fields exist in Propertybase it leads to significant errors.
Click here to learn more.
If you need assistance with this matter, please contact Propertybase Support.
Please include your org ID (00D5Z00000123456) in your support message.
Your Propertybase Team
The above message is telling you, that there are two fields on an object with the same Field Name also known as API (Field) name. You will need to find those two fields on the object in "Fields & Relationships" in Object Manager>Object>Fields & Relationships and change the API Field name of one of them.
Also note: prefixes from installed packages like pba__ are fully ignored by the system, so pba__Property__c and Property__c are considered duplicates.
In the above example, you would find the fields that have "Property__c" in the API name. So you can't look for them via their label or use the Quickfind box (as that will also only find the labels).
Solution Approach 1:
Either make sure you have loaded all fields by scrolling all the way to the bottom of the "Fields & Relationships" page and you see the full field count at the top (screenshot shows "180 Items") and then you use "Find in Page" (CMD-F or Ctrl-F) to search for the field name string "Property__c":
Or you switch to "Classic", find the object in Setup>Objects>Listings and search that page for the field name string (see also this article on API Field Names):