I was following a tutorial online, but the authour did not specify that I had to create another dataset for the parameter. so I

https://social.msdn.microsoft.com/Forums/sqlserver/en-US/6ce3fbaa-bc6d-4411-bb1f-aaecaaede3cc/ssrs-passing-multivalued-parameters-to-mdx?forum=sqlreportingservices

then cretaed another dataset for the parameter and was able to use it, I dont know if its the right way but it worked. Also the hidden dataset is still not coming up.

Thanks