Using parameter table to make new column

Hi,

I have a table Booking imported from an Excel file

 
I want to add a new column Report_Commission using a table Commission_Parameters I created by using "Enter data": 

 The two tables are linked:

To add the new column, I use "New Column" in the Home tab

Report_Commission = IF(Booking[Code]="A";Booking[Memberschip]+Booking[Installment]*0,25/0,0925;Booking[Commission])

Question 1: Why can't I find the table Commission_Parameters in the autocompletion?

Question 2:

When I explicitly add the two fields from Commission_Parameters:

Report_Commission = IF(Booking[Code]="A"; Booking[Memberschip] + Booking[Installment] * Commission_Parameters[Commission%] / Commission_Parameters[Tax%]; Booking[Commission])

why do I get the error:  "A single value for column 'Commission%' in table 'Commission_Parameters' cannot be determined. This can happen when a measure formula refers to a column that contains many values without specifying an aggregation such as min, max, count, or sum to get a single result."?

Question 3: Why does this error persist even when I add an aggregation to the fields Commission_Parameters[Commission%] and Commission_Parameters[Tax%]?

Thanks,

R.W.