When you are adding the RepID to the linkTemp you are concatenating. This does not create an association with the transactions. If you look at your link table data you will see what I mean. I suggest using a left join to the linked table.
GL_ID as %GL_ID,
Customer_ID as %CUSTOMER_ID,
Transdate as DateKey
Left Join(LinkTemp) //This is the line I added.
ID as %CUSTOMER_ID,
RepID as VertegenwoordigerKey
It's been a while ago, but I still have an issue with my link table. The issue I described at first is solved, thanks to your answer, but what I miss right now are the customers who don't have any transactions. What I would like to do is show all the customers per salesrep, by using the Link table. Due to the left join, I can't get all the customers linked to the salesrep because there are no transactions. I strongly hope you do have any options for me. Thanks in advance.