Parameter With IN Clause

in simple my query looks like

SELECT Field1, Field2
from table1
where table1.Field2 in (1,2,3)

and now i need to parameterize this query.... I tried with

SELECT Field1, Field2
from table1
where table1.Field2 in ([Parameter])

Now the problem is... it is working fine with only one value
For example if I input 1, it provide the required result. however, if I input 1,2 it doesnt provide a single recordset

I changed the datatype of parameter from number to text and also tried different way of inputting number like "1,2" , 1,2, but still problem is the same...

Can someone please guide me where I am going wrong

Thanks in advance