The problem is not at the procedure it is at the calling. When you call the stored procedure, you need to declare and pass in the required parameter
declare @NAME VARCHAR(50),
@CITY VARCHAR(200),
@MOBILE NUMERIC(20)
execute GETDETAIL @AGE = 21,
@NAME = @NAME OUTPUT,
@CITY = @CITY OUTPUT,
@MOBILE = @MOBILE OUTPUT
SELECT @NAME, @CITY, @MOBILE
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solved This procedure not working