How to escape the "\" character in Advanced Query SQL for against SQL Server?

How to escape the "\" character in Advanced Query SQL for against SQL Server?

I am trying to use the following expression in an Advanced Query SQL
 SUBSTRING(SMSTopConsoleUser, 1, CHARINDEX('\', SMSTopConsoleUser) - 1) as SMSTopConsoleUserDomain  

It executes correctly when ran on the SQL Server however Outsystems escapes the "\" as "\\" which causes the statement to fail.
I tried changing it to "\\" in my expression but that just gets interpreted to "\\\\".
How can I prevent this from happening?

We are running on platform 9.1.605.0

Should work if you remove -1

SUBSTRING(SMSTopConsoleUser, 1, CHARINDEX('\', SMSTopConsoleUser) ) as SMSTopConsoleUserDomain

I tried that, which doesn't address the issue I am having.

The character \ in the SQL tab of gets changed to \\ when viewing Executed SQL tab no matter where it exists in a query.

How about this. Add a parameter call it Slash. Set Expand Inline to Yes. Set value to "'\'" ..note the single quotes within the double quotes.
My query is like this

SELECT SUBSTRING({Customer}.[FirstName], 1, CHARINDEX(@Slash , {Customer}.[FirstName])) as SMSTopConsoleUserDomain From {Customer}

Then the executed SQL looks like this.
SELECT SUBSTRING( [OUTSYSTEMSSANDBOX].DBO.[OSUSR_TRG_CUSTOMER].[FIRSTNAME], 1, CHARINDEX('\' , [OUTSYSTEMSSANDBOX].DBO.[OSUSR_TRG_CUSTOMER].[FIRSTNAME])) as SMSTopConsoleUserDomain From [OUTSYSTEMSSANDBOX].DBO.[OSUSR_TRG_CUSTOMER]