Compare Dates between two differente tables in DAX

Hello, I'm trying to compare two dates between 2 different tables, but it seem's the second table is not bringing any value os is giving error.

IF('fMarketing Campaigns Sales'[Date] = SELECTEDVALUE('dimCampaigns Data'[Start date ]), "SAME", "DIFFERENT")

The tables have a many to many relantionship with both cross filter direction.

Could someone help me?