Dynamic constant line for scatter plot based on parameter values

Hi , xariet 

According to your description, you want to add a constant line in your visual and you get an error code .

I test it in my side , when using your dax code , i get the same error in my side .

For this , it seems we can not use the SELECTEDVALUE() function to get the slicers' selection.

You can try to use this dax code and we can meet your need:

choose Value = IF(
     MAX('Choose measure 2'[Pick measure])="LTV ratio",
    40,
    IF(
        MAX('Choose measure 2'[Pick measure])="Borrower Debt to Income Ratio",
        80,
        IF(
            MAX('Choose measure 2'[Pick measure])="Amount Borrowed",
            150000,
            0
        )
    )
)

Thank you for your time and sharing, and thank you for your support and understanding of PowerBI! 

Best Regards,

Aniya Zhang

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