Using substitution variable in Management reporting

I have created a substitution variable named (&sv_prg) and assigned multiple individual members to it say (p_100, p_110, p_200) it is not a range.
When I'm editing/working with the report, I get an error that the substitution variable is not found in the source, but these members do exist in the source cube. (which means the validation of substitution variable failed)
I cannot use : or :: separator for these members, because it's not a range. What is the correct format to define multiple individual members?