DAX Error: A function 'PLACEHOLDER' has been used in a True/False expression that is used as a table

Hi Anonymous   I'm finding it hard to understand what you're trying to acheive.  To help with your wider goal it would be useful if you can post a picture of your model and provide some sample data in table format, or share the .pbix if you can.

A high-level description of what you're trying to do would help as well.

Some general comments on the code that may help you:

• Is the uoa_payslips_history_aggregated[YearMonth] column a date or datetime type?  It needs to be to use the DATEDIFF function
• Best practice is to not use SUMMARIZE to add columns.  See https://www.sqlbi.com/articles/all-the-secrets-of-summarize/

You could refactor step 2 as

forecasting_uoa_payroll_step2 = 
    ADDCOLUMNS( 
        VALUES(forecasting_uoa_payroll_step1[Country]),
        "UoA Per Customer Average", CALCULATE(AVERAGE(forecasting_uoa_payroll_step1[UoA_per_Customer]))
    )

• However, I don't understand why you're doing that step.  Using this as a filter in CALCULATE/CALCULATETABLE isn't going to have any effect.  You calculate an average but then do nothing with it.  What are you trying to do here?
• It also references this: forecasting_uoa_payroll_step1.  Does that exist now you've combined step1 and step 2 together?
• You say the ultimate aim is to create one table, but I don't see how Step 2 and Step 3 are in any way related