Must declase Scaler Variable error on Multiselect parameter when I use IN statement in SP ?

HiI am using a multiselect parameter @DiagnosisType My sp states ... ALTER PROCEDURE [dbo].[..._count]@StartDate datetime,@EndDate datetime,@Costcenter varchar(3),@DiagnosisType varchar(100)ASSELECT .....where (dbo.ClinicalType.Code in (@DiagnosisType))ThanksJoein (@DiagnosisType))@DiagnosisType nvarchar(max)