Arithmetic overflow error converting expression to data type datetime when running dynamic sql

I have seen a couple solutions to this SQL error(8115) but none seems to work for me. I think its because I am using dynamic SQL script. I dynamically pull data from multiple servers that have the same structure and insert into a central table. The issue I have having is that when using dynamic script as seen below I keep getting an error.

DECLARE @SQL NVARCHAR(4000); DECLARE @counter int = 0; DECLARE @scriptcnt int; declare @startdate varchar(8) = '20180304';-- cast(@startdate as date) declare @enddate varchar(8) = '20180305';--cast(@enddate as date) select srv.name INTO #ServerNames from sys.servers srv where name like 'Pulse%' order by 1; select name,right(name,5) store_no into #locationCode from #SERVERNAMES; With ServerCTE AS ( SELECT Root=NAME + '.[POS].[dbo].' FROM #SERVERNAMES) Select Root + '[Customer]' as Customer INTO #Tables from ServerCTE Begin Transaction delete from WFLCustomerMaster --where Location_Code = '16450'--@storeNum commit; select ' Begin TRY Begin Transaction Insert into WFLCustomerMaster(.....) SELECT ..... FROM '+ Customer + ' where [Last_Order_Date] between '+ @startdate+ ' and '+ @enddate+ ' [This line is the issue] commit; END TRY BEGIN CATCH SELECT ERROR_PROCEDURE() as nameofprocedure, ERROR_NUMBER() AS errorcode, error_line() as errorline, ERROR_MESSAGE() as errormessage END CATCH' as Customer into #query from #Tables a, #locationCode b where left(a.Customer,13) = b.name select @scriptcnt = count(*) from #query while @counter < @scriptcnt begin set @counter = @counter + 1 SET @SQL = (SELECT Customer FROM (SELECT ROW_NUMBER() OVER (ORDER BY Customer) AS ID, Customer FROM #query) MySQL WHERE ID=@Counter ) EXEC SP_EXECUTESQL @SQL end 

I tried converting @startdate and @enddate to date, datetime and datetime2 but nothing works. I realize that when I hard code the date it works as per below:

...'where [Last_Order_Date] between ''20180306'' and ''20180306'''.... 

So I know that this part is the issue. Can someone assist?