A table of multiple values was supplied where a single list was expected

[fe_username]

Dear Guru of PowerBI,
I've a data model with two tables "Billing" and "Amount" related through a many-to-many relationship through "key"
My dax formula 

Totale Fatturato = LOOKUPVALUE(Billing[amount],Billing[key],[key]) + Summary[Amount Year]

It started to give me this error "A table of multiple values was supplied where a single list was expected".

How could it be solved?

[fe_username · Accepted solution]

Don't know totally why that happened, but I figured out that our client had an outdated version of PowerBI and after updating the issue fixed itself.

[halfglassdarkly]

Is Lookupvalue the right formula to use here? Are you wanting to lookup a single value or if multiple records exist in the Billing table do you want to sum [Amount]?

If you're wanting to sum then I'd use Calculate instead:

Calculate(Sum(Billing[Amount]),Billing[Key]=[Key])

[Riddhi_06]

Hi,
You can create a composite key in both the tables which will have unique values and then try Lookup function.
Composite key can be created by concatenating values of two or more columns into one column. But make sure those columns should be present in both the tables.