Measure to sum unique values in column with duplicate values based on a another column

[Datafruit]

Hi guys

Pretty new to PBI and have a problem with creating a measure, that does what I need it to do. Basically I have a table where I have a bunch of data and I need to sum "Transaction fee" column, but since there are multiple entries for one customer in one country, the transaction fee is also "duplicated". And if I sum it up like this, then for the highlighted instance, the amount would be 4x bigger, which is a BIG NO NO 😄

Anyway, I hope you can help, since I've spent like a good 2,5h on this and searched and tried different options that people have posted, but without luck. 
So it would need to be a measure, other columns used in slicer should be able to affect the result. And here is a sample data set if some of you might be interested.
Sample data 

Thanks a lot

[Greg_Deckler · Accepted solution]

@Datafruit Perhaps:

Measure =
  VAR __Table = 
    DISTINCT(
      SELECTCOLUMNS('Table',"fee",[transaction_fee],"nr",[customer_nr],"country",[country])
    )
RETURN
  SUMX(__Table,[fee])

[m61allison]

This solution looks like it will fit for my data issues as well, however I cannot get correct syntax to work for the Measure.  Can you help with the VAR command and when we say "Table" are we referring to the table with my data or some temporary table?

[Datafruit]

@Greg_Deckler Works, thank you! 🙂