The field 'Property__c' either does not exist on the Offer__c object or it is not a Master-Detail relationship.

Hi @Sathiya Mohan -  

I found out the issue. I was creating my Master & Lookup relationship in the wrong custom object. It was supposed to be in the "Offer" object that I made previously.

https://trailhead.salesforce.com/trailblazer-community/feed/0D54V00007RHHke

In this situation you need to follow below steps:-

Firstly create a new playground Now create a Custom object called Offer and create another Custom object called Property in Object Manager In Property custom object create Look-up relationship for Contact and then in Offer custom object create Main- detail relationship for property and look-up for contacts as well.

https://trailhead.salesforce.com/en/trailblazer-community/feed/0D54S00000HFODX