SQL Fill in 0 for the rows with no data

I am trying to generate a table that have receipt count group by days of the week and every hour of a day. I want the table include the day and hour that have no record and will fill it in with 0 for the receipt count. For example, I want the query to return a table with something like this:

And the rest of the table will resume with Tuesday, Wednesday and so on until Sunday with every hour of a day in the table as above. The day of the week is generated with DATENAME() function and the hours of the day is generated with CTE as I don't have a table for the weekdays and hours. My query as of now will only return results with days and hours that have records in the database. My query is as below:

with mycte as
(
    SELECT 0 AS MyHour
    UNION ALL
    SELECT MyHour + 1
    FROM mycte 
    WHERE MyHour + 1 < 24
)
SELECT h.SalesDay, FORMAT(DATEADD(hour,mycte.MyHour,'00:00'),'HH:mm') AS SalesByHour, COALESCE(ReceiptCount,0) AS HourlySales FROM mycte
LEFT JOIN
(
SELECT
   DATENAME(WEEKDAY, TRANDATETIME) AS SalesDay,
   DATEPART(hour, TRANDATETIME) AS SalesByHour,
   COUNT(REF) as ReceiptCount
FROM [RC_BACK].[dbo].[TRAN]
WHERE TRANCODE = 'SA'
GROUP BY DATENAME(WEEKDAY, TRANDATETIME), DATEPART(hour, TRANDATETIME)
) h
ON h.SalesByHour = mycte.MyHour
ORDER BY h.SalesDay, SalesByHour ASC

and results are as below:

What do I need to add for my query so that it will have the results that I want?

As @DaleK indicated an ideal solution would be to use a sort of calendar table with days and hours and use it in the code. Here is a solution using the CTE route you have used :

WITH cte_hours
AS (
SELECT 0 AS [hour]
UNION ALL
SELECT [hour] + 1
FROM cte_hours
WHERE [hour] + 1 < 24)
,cte_days
AS (
SELECT daynm, [dayname]
FROM (
VALUES 
(0,'Monday')  ,(1,'Tuesday') ,(2,'Wednesday') ,(3,'Thursday') ,(4,'Friday') ,(5,'Saturday') ,(6,'Sunday')
)  a(daynm, [dayname])
)
/*Sample sales data set */
, cte_sales
AS (
SELECT [hour], [dayname], [hourlysales]
FROM (
VALUES 
(4,'Monday', 100), (14,'Monday', 110), (5,'Monday', 20), (6,'Monday', 10), (21,'Monday', 3),(3,'Monday', 50)
,(11,'Tuesday', 3), (12,'Tuesday', 15),  (9,'Tuesday', 155), (2,'Tuesday', 25)
,(12,'Wednesday', 125) ,(14,'Wednesday', 9) ,(11,'Wednesday', 95) 
,(13,'Thursday', 42), (23,'Thursday', 342), (6,'Thursday', 123)
,(20,'Friday', 9),(4,'Friday', 93)
,(15,'Saturday', 32),(12,'Saturday', 322),(16,'Saturday', 132),(19,'Saturday', 2),(5,'Saturday', 3),(3,'Saturday', 323)
,(18,'Sunday', 65) ,(13,'Sunday', 165) ,(1,'Sunday', 5) ,(14,'Sunday', 665)
)  a([hour], [dayname], [hourlysales])
) 
SELECT dy.[dayname], hr.[hour] ,FORMAT(DATEADD(hour,hr.[hour],'00:00'),'HH:mm') As formathr
, ISNULL([hourlysales], 0) AS [hourlysales]
FROM cte_hours hr
CROSS JOIN cte_days dy
LEFT OUTER JOIN cte_sales sl ON sl.[hour] =  hr.[hour] and sl.[dayname] =  dy.[dayname]
ORDER BY dy.daynm, hr.[hour];