Many-to-many relationship using a bridge table?

Hello, I have the following data model: a dimensional table that links to the fact table using the "Marketing ID" field. The problem is the "Marketing ID" field in the dimensional table is not unique, so I have to set up a many-to-many relationship. I'd like to analyze the sales amount by customer state, but the problem is I get duplicate values in the matrix. The total sales amount for all the transactions is $846, but the sum of the individual values in the matrix does not equal $846, most likely because of duplicate values. Would anybody know how to solve this scenario? Would a bridge table help in this scenario? If yes, how can I set this up to avoid double counting sales?