Replacement path variable

Hi experts

I have an interval variable on char 0FS_BDATE (reference char 0DATE).

I try to create a variable on char 0CALDAY (reference char 0DATE) as replacement path variable on the interval variable of FS_BDATE.

But when defining the replacment rule for variable, the variable of FS_BDATE is not listed.

Any error in reasoning?

Thanks