Dynamic Pivot As Function, Table Function Or Stored Procedure - function

Question

I have a table that was created to show a client's areas in rows not columns. I created a pivot as a solution for this. I understand that there are other options like CASE statement and JOINS that might also work. The next step was to see if I can add it to a function or Stored Procedure. I was not able to find something to help me with functions or table functions that was easy to understand, or I am too stupid. I did create a SP, but I can't seem to use it within a SELECT statement as per some blogs I read. So, to all the experts out there what is the best practice to make sure I do this effectively.
DATA EXTRACTION BEFORE
DATA EXTRACTION WITH PIVOT
The above is the data I extracted from one client - I will have anything from 10K to 50K records if not more. Not sure if that is relevant?? But the issue is that I need to link it to the client table and address table and and....
Below is my pivot attempt and my SP attempt as well as my Table Function.
Then when I try to do a table function, I get this error as per >>> [![PIVOT TABLE FUNCTION](https://i.stack.imgur.com/WWDhq.png)](https://i.stack.imgur.com/WWDhq.png)
Also this error: Invalid use of a side-effecting operator 'EXECUTE STRING' within a function
If anyone can point me in the right direction or advise me what I need to look for to continue my google search, I would and will really, really appreciate it.
Thanks
> SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- ======================================================
-- Author: Stefan Kleinhans
-- Create date: 02-11-2022
-- Description: Supplying client areas in single columns
-- ======================================================
CREATE FUNCTION [crm].[UDF_GetClientAreas_Gain] (#AreaGroup Varchar(10), #TenantId INT)
RETURNS #T TABLE
(
TenantID INT,
CustID INT,
Division Char(2),
Technical Char(3),
SubDivision Char(3),
MainArea Char(3),
SubArea Char(3)
)
AS
BEGIN
DECLARE #FieldList varchar(1000)
/****** Script for SelectTopNRows command from SSMS ******/
SELECT #FieldList = CONCAT('[',STRING_AGG([AreaType],'],['),']')
FROM (
SELECT DISTINCT [AreaType], GroupLevel
FROM [Xyro_ADF].[crm].[dimClientAreas]
WHERE AreaGroup = #AreaGroup
AND AreaType <> 'Division'
) a
DECLARE #Str varchar(max)
SET #Str = 'SELECT TenantID, CustID, Division, ' + #FieldList + ' FROM
(
SELECT TenantID, CustID, Division, AreaType, AreaName
FROM [Xyro_ADF].[crm].[dimClientAreas]
WHERE AreaGroup = ''' + #AreaGroup + '''
AND TenantID = ' + CONVERT(varchar,#TenantId) + '
) AS DataTbl
PIVOT
( MAX(AreaName) FOR AreaType IN (' + #FieldList + ')
) AS PVTbl'
--PRINT(#Str)
EXEC(#Str)
RETURN
END
USE [Xyro_ADF]
GO
/****** Object: StoredProcedure [dbo].[usp_ClientArea_Pivot] Script Date: 28/10/2022 07:19:53 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- ====================================================================================
-- Author: Stefan Kleinhans
-- Create date: 28-Oct-2022
-- Description: A procedure that uses dynamic SQL for a PIVOT operation
-- ====================================================================================
CREATE PROCEDURE [dbo].[USP_ClientArea_Pivot]
(#TenantID INT,
#CustID INT)
AS
BEGIN
DECLARE
#Col VARCHAR(MAX),
#Str VARCHAR(MAX)
SET NOCOUNT ON
SET #Col = (SELECT STRING_AGG(AreaType, ', ') FROM (SELECT DISTINCT AreaType FROM [Xyro_ADF].[crm].[dimClientAreas] WHERE AreaType <> 'Division') AS x)
SET #Str =
'SELECT AreaGroup, Division, '+ #Col +'
FROM
(SELECT TenantId, CustId, AreaGroup, Division, AreaType, AreaName
FROM [Xyro_ADF].[crm].[dimClientAreas]) AS Source_Table
PIVOT
(MAX(AreaName) for AreaType IN ('+ #Col +')
)as Pivot_Table
WHERE TenantId = '+ CONVERT(VARCHAR,#TenantID) +'
AND CustId = '+ CONVERT(VARCHAR,#CustID) +' '
EXEC (#Str)
SET NOCOUNT OFF
END
GO
/* EXECUTE SP WITH #TenantId & #ClientId */
--EXEC [dbo].[usp_ClientArea_Pivot] 1,33395