Joining 4 table in order to produce one master table

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SQL

T-SQL

I'm trying to add a new code to an already existing code that join 3 tables, but I'm having trouble running it. The goal is to add a table to the code that is producing a table. Here is the original code:
I have this code WHICH IS JOIN OF 3 TABLES,

SELECT 
 [Provider] AS Publisher
,[Price_Rate]
,[Source_ID]
,Media.Date
,Media.Impressions
,Media.Clicks
,'0' AS [Opt-buyers]
,'0' AS [Completed buyers]
,Media.accounting
FROM [dbo].[budget]  AS BUDGET

LEFT JOIN 
(

  SELECT CASE WHEN [Ad_Set_Name] LIKE 'tw_%' 
  THEN'twitter' 
  WHEN [Ad_Set_Name] LIKE 'IN_%'
  THEN 'insta'
   ELSE '?'
      END AS Publisher
  ,CAST([Day] AS Date) AS Date
  ,SUM(CAST([Impressions] AS INT)) AS Impressions
  ,SUM(CAST([Link_Clicks] AS INT)) AS Clicks
  ,SUM(CAST([Amount_Spent__USD_] AS money)) AS Spend
  FROM [dbo].[twitter]
  Group by Day,[Ad_Set_Name]

   UNION ALL

    SELECT CASE WHEN [Site__PCM_] = 'acuits.com'
    THEN 'acqt'
     WHEN [Site__PCM_]= 'PulsePoint'
     THEN 'plpt'
    WHEN [Site__PCM_] = 'SRAX'
    THEN 'srax'
    ELSE [Site__PCM_]
    END AS Publisher
    ,CAST(Date AS Date) AS Date
    ,SUM(CAST(impressions AS INT)) AS Impressions
     ,SUM(CAST(clicks AS INT)) AS Clicks
    ,SUM(CAST(media_cost AS money)) AS Spend
   FROM [dbo] [pcm]
   Group by [Site__PCM_]
  ,Date

 ) AS new_sources_budget
 ON BUDGET.Source_ID = Media.Publisher
  WHERE source_id IS NOT NULL

and I'm trying to join another table **called Email** to what's this code is currently providing, but
I'm having tough time passing thus far. the goal is to add this code

SELECT 
  SUM(CAST(_Send2 AS INT)) AS [Email Sent]
 ,SUM(CAST(_Open2 AS INT)) AS [Email Open]
 ,SUM(CAST(Click2 AS INT)) AS [Email Click]
FROM [dbo].[behaviour]
Group by _Send2,_Open2,Click2

This code provide the following table
Publisher Source_ID Date Impression clicks optin Spend
accuea 1010 4/20/20 updown 10 yes 300

any help will be appreciated.

What I have tried:

I have tried to add this code to the current code but it doesn't work

 [Provider] AS Publisher
,[Price_Rate]
,[Source_ID]
,Media.Date
,Media.Impressions
,Media.Clicks
,'0' AS [Opt-buyers]
,'0' AS [Completed buyers]
,Media.accounting
FROM [dbo].[budget]  AS BUDGET

LEFT JOIN 
(
      SUM(CAST(_Send2 AS INT)) AS _Send2
      ,SUM(CAST([_Open2] AS INT)) AS _Open2
      ,SUM(CAST([Click2] AS money)) AS Click2
 FROM [dbo].[Email]
  Group by _Send2,_Open2,Click2

UNION ALL

  SELECT CASE WHEN [Ad_Set_Name] LIKE 'tw_%' 
  THEN'twitter' 
  WHEN [Ad_Set_Name] LIKE 'IN_%'
  THEN 'insta'
   ELSE '?'
      END AS Publisher
  ,CAST([Day] AS Date) AS Date
  ,SUM(CAST([Impressions] AS INT)) AS Impressions
  ,SUM(CAST([Link_Clicks] AS INT)) AS Clicks
  ,SUM(CAST([Amount_Spent__USD_] AS money)) AS Spend
  FROM [dbo].[twitter]
  Group by Day,[Ad_Set_Name]

   UNION ALL

    SELECT CASE WHEN [Site__PCM_] = 'acuits.com'
    THEN 'acqt'
     WHEN [Site__PCM_]= 'PulsePoint'
     THEN 'plpt'
    WHEN [Site__PCM_] = 'SRAX'
    THEN 'srax'
    ELSE [Site__PCM_]
    END AS Publisher
    ,CAST(Date AS Date) AS Date
    ,SUM(CAST(impressions AS INT)) AS Impressions
     ,SUM(CAST(clicks AS INT)) AS Clicks
    ,SUM(CAST(media_cost AS money)) AS Spend
   FROM [dbo] [pcm]
   Group by [Site__PCM_]
  ,Date

 ) AS new_sources_budget
 ON BUDGET.Source_ID = Media.Publisher
  WHERE source_id IS NOT NULL

and I'm trying to join another table **called Email** Highlighted in Bold, but
I'm having tough time passing thus far. the goal is to add this code
When adding that the code highlighted in bold, I get the following error

All queries combined using a UNION, INTERSECT or EXCEPT operator must have an equal number of expressions in their target lists.

SELECT 
  SUM(CAST(_Send2 AS INT)) AS [Email Sent]
 ,SUM(CAST(_Open2 AS INT)) AS [Email Open]
 ,SUM(CAST(Click2 AS INT)) AS [Email Click]
FROM [dbo].[behaviour]
Group by _Send2,_Open2,Click2