Looking for an alternative to a CTE that will work as a subquery in IF EXISTS

I have an IF EXISTS 'upsert' running fine by itself in it’s own stored proc. But when I try and use the same statement referencing a CTE, it doesn't recognize the CTE. I see in related post that I'm not allowed to use the CTE as the subquery. I'm curious why is that, and how else could I accomplish this?

Working stored procedure using IF EXISTS:

ALTER Procedure [dbo].[sproc_receive]    @StockCode VARCHAR(50),     @Qty DECIMAL(18,6)AS--source: https://weblogs.sqlteam.com/dang/2007/10/28/conditional-insertupdate-race-condition/SET NOCOUNT, XACT_ABORT ONBEGIN TRANIF EXISTS(SELECT * FROM tblReceivedQty WITH (UPDLOCK, HOLDLOCK) WHERE StockCode = @StockCode)    BEGIN          UPDATE tblReceivedQty          SET ReceivedQty = ReceivedQty + @Qty          WHERE StockCode = @StockCode    ENDELSE    BEGIN          INSERT INTO tblReceivedQty (StockCode, ReceivedQty)          VALUES (@StockCode, @Qty)    ENDCOMMITRETURN @@ERRORGO

And here is my attempt to repurpose the IF EXISTS in another stored proc which takes a json string as input.

USE [<databasename>]GO/****** Object:  StoredProcedure [dbo].[sproc_PutAway]    Script Date: 6/13/2022 4:14:02 PM ******/SET ANSI_NULLS ONGOSET QUOTED_IDENTIFIER ONGOALTER Procedure [dbo].[sproc_PutAway](@json NVARCHAR(MAX) = '')ASBEGIN-- Create CTE from JSON inputWITH json_received(StockCode, Qty)AS(SELECT StockCode, Qty    FROM OPENJSON(@json)    WITH (        StockCode VARCHAR(30) '$.StockCode',        Qty DECIMAL(18,6) '$.Qty'        ))SET NOCOUNT, XACT_ABORT ONBEGIN TRANIF EXISTS(SELECT * FROM tblReceivedQty WITH (UPDLOCK, HOLDLOCK) WHERE tblReceivedQty.StockCode = json_received.StockCode)    BEGIN        UPDATE tblReceivedQty        SET tblReceivedQty.ReceivedQty = tblReceivedQty.ReceivedQty - (            SELECT Sum(Qty)            FROM json_received            WHERE tblReceivedQty.StockCode = json_received.StockCode            GROUP BY json_received.StockCode            )    ENDELSE    BEGIN        INSERT INTO tblReceivedQty (StockCode, ReceivedQty)        VALUES (json_received.StockCode, (-1 * json_received.Qty))    ENDCOMMITRETURN @@ERRORGO

This gives me a syntax error after the CTE, and a 'multipart identifer could not be bound' on all references to the CTE.

Appreciate any hints!