KPI doesn't return any values?

Dear Expert,

"Accounts receivable turnover" KPI doesnt return any values,  I try to investigate why this happens? I go to https://technet.microsoft.com/en-us/library/jj710388.aspx  website to check the cubes structures.

I find below equation for  "Accounts receivable turnover" , I don't understand what is "Reference ID" and how to deal with it?

[Sales (Reference ID = 33) *-1] - Sales Returns and Discounts (Reference ID = 34) / [Beginning Accounts Receivable (Reference ID = 4) + Ending Accounts Receivable (Reference ID = 4) / 2]

Please any help.

Regards,