I had been trying to get a multi valued parameter into a linked report for the longest time, and when running the report all I would get was an error, “The %variable% is missing a value”.

I just couldn’t figure it out, but it was just me being dumb. The answer is really quite simple:

 

I was trying to enter my values like this:

value1, value2, value 3

 

But what you need to do is enter them separately on a different line:

 

Then SSRS will make a comma delimited list of them for you.