@CreatedAt is an input parameter to your SP, so when you call it you have to provide the data to fill it. The error doesn't occur when you creta ethe SP, it happens when you call it. So try:
EXEC dbo.spAddVoucherCheck @CreatedAt='Hello', ...
BTW: the name @CreatedAt implies this is date based data: if so then don't store it as NVARCHAR - use a DATETIME field instead - it makes everything you do with the data later a lot, lot easier. As a result, the @CreatedAt parameter to your SP should be DATETIME as well.