Sumx formula giving error for one record

[UmairKamal]

Dear Users,

I have been racking my brains over this issue since yesterday. any help will be greatly appreciated.

I have two tables in Power BI, Case Table and Paid Table. both are joined by a unique reference number highlighted in Green.  

In the Case Table, I have used a formula in Column G

Payment = SUMx(Paid, if(Paid[Ref-Event Month]=Case[Ref-Event Month], CALCULATE(SUM(Paid[Payment])),BLANK()))

I have over 7000 records, and all of them are correctly displaying the payment amount with the exception of one reference. 

I have checked over and over in the Paid Table, but all the amounts add up to £204, whereas the Case Table is showing £244 for this reference. 

[lbendlin]

Please provide sample data that covers your issue or question completely, in a usable format (not as a screenshot).
https://community.powerbi.com/t5/Community-Blog/How-to-provide-sample-data-in-the-Power-BI-Forum/ba-...
Please show the expected outcome based on the sample data you provided.

https://community.powerbi.com/t5/Desktop/How-to-Get-Your-Question-Answered-Quickly/m-p/1447523