I'm having issues executing a stored procedure. Basically, when I execute my stored procedure by itself, it works just fine, and returns the correct values. However, when I call the same stored procedure with a parameter and try to assign return value into a variable it doesn't return the correct value always return 0. Is there something weird going on with how the variables are handled? Or is something else going wrong? See my code below.

ALTER PROCEDURE [dbo].[NumbersToWords]
    @Number INT
AS
BEGIN
    SET NOCOUNT ON;

    SET @Number = ABS(@Number)
    DECLARE @vResult NVARCHAR(MAX) = '' 
    
    -- pre-data
    DECLARE @tDict TABLE (Num INT NOT NULL, Nam NVARCHAR(255) NOT NULL)
    INSERT 
    INTO    @tDict (Num, Nam)
    VALUES  (1,'one'),(2,'two'),(3,'three'),(4,'four'),(5,'five'),(6,'six'),(7,'seven'),(8,'eight'),(9,'nine'),
            (10,'ten'),(11,'eleven'),(12,'twelve'),(13,'thirteen'),(14,'fourteen'),(15,'fifteen'),(16,'sixteen'),(17,'seventeen'),(18,'eighteen'),(19,'nineteen'),
            (20,'twenty'),(30,'thirty'),(40,'fourty'),(50,'fifty'),(60,'sixty'),(70,'seventy'),(80,'eighty'),(90,'ninety')
    
    DECLARE @ZeroWord       NVARCHAR(10) = 'zero'
    DECLARE @DotWord        NVARCHAR(10) = 'point'
    DECLARE @AndWord        NVARCHAR(10) = 'and'
    DECLARE @HundredWord    NVARCHAR(10) = 'hundred'
    DECLARE @ThousandWord   NVARCHAR(10) = 'thousand'
    DECLARE @MillionWord    NVARCHAR(10) = 'million'
    DECLARE @BillionWord    NVARCHAR(10) = 'billion'
    DECLARE @TrillionWord   NVARCHAR(10) = 'trillion'

    -- decimal number   
    DECLARE @vDecimalNum INT = (@Number - FLOOR(@Number)) * 100
    DECLARE @vLoop SMALLINT = CONVERT(SMALLINT, SQL_VARIANT_PROPERTY(@Number, 'Scale'))
    DECLARE @vSubDecimalResult  NVARCHAR(MAX) = N''
    
    IF @vDecimalNum > 0
    BEGIN
        WHILE @vLoop > 0
        BEGIN
            IF @vDecimalNum % 10 = 0
                SET @vSubDecimalResult = FORMATMESSAGE('%s %s', @ZeroWord, @vSubDecimalResult)
            ELSE
                SELECT  @vSubDecimalResult = FORMATMESSAGE('%s %s', Nam, @vSubDecimalResult)
                FROM    @tDict
                WHERE   Num = @vDecimalNum%10

            SET @vDecimalNum = FLOOR(@vDecimalNum/10)
            SET @vLoop = @vLoop - 1
        END
    END
    
    -- main number
    SET @Number = FLOOR(@Number) 
    IF @Number = 0
        SET @vResult = @ZeroWord
    ELSE
    BEGIN
        DECLARE @vSubResult NVARCHAR(MAX) = ''
        DECLARE @v000Num DECIMAL(15,0) = 0
        DECLARE @v00Num DECIMAL(15,0) = 0
        DECLARE @v0Num DECIMAL(15,0) = 0
        DECLARE @vIndex SMALLINT = 0
        
        WHILE @Number > 0
        BEGIN
            -- from right to left: take first 000
            SET @v000Num = @Number % 1000
            SET @v00Num = @v000Num % 100
            SET @v0Num = @v00Num % 10
            IF @v000Num = 0
            BEGIN
                SET @vSubResult = ''
            END
            ELSE 
            BEGIN 
                --00
                IF @v00Num < 20
                BEGIN
                    -- less than 20
                    SELECT @vSubResult = Nam FROM @tDict WHERE Num = @v00Num
                    IF @v00Num < 10 AND @v00Num > 0 AND (@v000Num > 99 OR FLOOR(@Number / 1000) > 0)--e.g 1 001: 1000 AND 1; or 201 000: (200 AND 1) 000
                        SET @vSubResult = FORMATMESSAGE('%s %s', @AndWord, @vSubResult)
                END
                ELSE 
                BEGIN
                    -- greater than or equal 20
                    SELECT @vSubResult = Nam FROM @tDict WHERE Num = @v0Num 
                    SET @v00Num = FLOOR(@v00Num/10)*10
                    SELECT @vSubResult = FORMATMESSAGE('%s %s', Nam, @vSubResult) FROM @tDict WHERE Num = @v00Num 
                END

                --000
                IF @v000Num > 99
                    SELECT @vSubResult = FORMATMESSAGE('%s %s %s', Nam, @HundredWord, @vSubResult) FROM @tDict WHERE Num = CONVERT(INT,@v000Num / 100)
            END
            
            --000xxx
            IF @vSubResult <> ''
            BEGIN

                SET @vSubResult = FORMATMESSAGE('%s %s', @vSubResult, CASE 
                                                                        WHEN @vIndex=1 THEN @ThousandWord
                                                                        WHEN @vIndex=2 THEN @MillionWord
                                                                        WHEN @vIndex=3 THEN @BillionWord
                                                                        WHEN @vIndex=4 THEN @TrillionWord
                                                                        WHEN @vIndex>3 AND @vIndex%3=2 THEN @MillionWord + ' ' + RTRIM(LTRIM(REPLICATE(@BillionWord + ' ',@vIndex%3)))
                                                                        WHEN @vIndex>3 AND @vIndex%3=0 THEN RTRIM(LTRIM(REPLICATE(@BillionWord + ' ',@vIndex%3)))
                                                                        ELSE ''
                                                                    END)

                SET @vResult = FORMATMESSAGE('%s %s', @vSubResult, @vResult)
            END

            -- next 000 (to left)
            SET @vIndex = @vIndex + 1
            SET @Number = FLOOR(@Number / 1000)
        END
    END--ok
    SET @vResult = FORMATMESSAGE('%s %s', RTRIM(LTRIM(@vResult)), COALESCE(@DotWord + ' ' + NULLIF(@vSubDecimalResult,''), ''))
    
    
    -- result
    SELECT UPPER(@vResult) AS 'Result'

END

This SQL query perfect

declare @number INT = 1520123
exec spWebNumbersToWords @number = 1520123

But when I try to run this SQL

declare @number INT = 1520123
declare @str nvarchar(max)
exec @str = NumbersToWords @number = 1520123
select @str as 'Word'

return 0 for @str

What am I missing here?