Conversion failed when converting the nvarchar value 'ALFKI' to data type int

Transact-SQL
1

ALFKI is the CustomerID in the Northwind database of MS SQL SERVER

Create proc Siparisler
(
@ContactName nvarchar(30)
)
as
select o.OrderID from Orders o 
inner join Customers c on c.CustomerID = o.OrderID
where c.ContactName like '%' + @ContactName + '%'

exec Siparisler 'A'

I get
Conversion failed when converting the nvarchar value 'ALFKI' to data type int.
error how do I solve this?
I tried using
exec Siparisler @ContactName = 'A'
though things like this did not work...

2

You're joining CustomerID to OrderID, they are different data types, and you probably intended to join to Orders.CustomerID.