This field is coming from the expression and I am not entering it manually.So, it seems if its been used once, then after that the system is taking only the field name and not the schema and therefore its ID_18_Digit_Format__c and not [Contact/ID_18_Digit_Format__c].
@id is my auto generated Adobe Primary key and ID_18_Digit_Format__c is the unique key. Both are different.
I am not very confident on mapping these as my requirement is to update 2 fields on SF based on the ID_18_Digit_Format__c field present.
Could not even find any document which describes these.