EXEC sp_executesql will work with Integers but not VarChars

I'm using EXEC sp_executesql for a dynamic query in SQL Server 2017.

I've tried various testing scenarios, and I can get results in my query (for other parameters) as long as the values passed in are Integers. So, that means, Location and Department testing works. However, I can't figure out if there's something I need to do differently for when I'm sending a NVARCHAR or DateTime.

Here's my stored procedure, with the NVARCHAR param. Do you see anything I'm doing wrong?

(
@tktitle NVARCHAR(200)
)

AS
BEGIN

Declare  @SQL NVARCHAR(MAX)

Set @SQL = 'SELECT        timekeep.tkinit, timekeep.tkfirst, timekeep.tklast, 
                         timekeep.tkemdate, timekeep.tktitle, timekeep.tkloc, timekeep.tkdept

FROM   abc.xyz'        
                     


IF @tktitle IS NOT NULL
Select @SQL = @SQL + 'AND ([tktitle] = @tktitle)'
EXEC sp_executesql @SQL, N'@tktitle varchar',  @tktitle


END

I can identify at least three issues:

• You need to specify a length for varchar when passing it as a parameter.
• You also need a space before the AND and the AND should be a WHERE.
• You need to assign the parameter in the execute call.

So:

IF @tktitle IS NOT NULL
    Select @SQL = @SQL + ' WHERE ([tktitle] = @tktitle)';
-------------------------^ separator
EXEC sp_executesql @SQL, N'@tktitle varchar(200)', @tktitle=@tktitle;