Size property has an invalid size of 0

If you are using Dapper, you have passed in a null value for the parameter, where the expected input was a string.

To find the offending value and it's parameter, inspect at the Dapper DynamicParameters object during a debug session and open the parameters being index referred to.

Yes, have to define the length for varchar / nvarchar data type like below.

cmd.Parameters.Add("@Description", SqlDbType.VarChar, 150).Direction =
    ParameterDirection.Output;

You need to define a length when specifying the varchar parameter:

SqlParameter job1 = cmd2.Parameters.Add("@job", SqlDbType.VarChar, 50);

You should use the same length as defined in your SQL Server stored procedure.

And btw: if your stored procedure also has no length defined (something like @job VARCHAR OUTPUT) - then you've defined a varchar string of 1 character length ......