Insert and return Automatically generated AlphaNumeric number from Stored Procedure in SQL Server

Hi,

I am creating a feedback form where I want to show the Feedback id to the user after the user submits his data.With your help I have created the required Store Procedure.But I am not able to return the value to user,when i try to do it it gives a error stating that cannot use output in declare statement.How do I achieve this.Here's my SP and C#

create table tbl_feebback
(
	Id int identity (1,1),
	FeedbackId varchar(10),
	[Message] varchar(max),
	CreatedDate Datetime
)


Create PROCEDURE [dbo].[usp_UserFeedback]
	@Message varchar(max)
	
AS
BEGIN
	SET NOCOUNT ON;
	BEGIN
		DECLARE @AlphaId VARCHAR(10)
		DECLARE @Count INT
		SELECT @Count = COUNT(*) + 1 FROM tbl_feebback 
		SET	@AlphaID = 'FB00' + LEFT(CAST(@Count AS VARCHAR(10)), 4)
		INSERT INTO [tbl_feebback]
			   ([FeedbackId]
			   ,[Message]
			   ,[CreatedDate]
				)
		VALUES
			   (@AlphaID
			   ,@Message
			   ,GETDATE()
				)
     END
END

 Code Behind

protected void InsertFeedback(object sender, EventArgs e)
        {
            String constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
            using (SqlConnection connection = new SqlConnection(constr))
            {
                SqlCommand command = new SqlCommand("usp_UserFeedback", connection);
                command.CommandType = CommandType.StoredProcedure;
                command.Parameters.AddWithValue("@Username", txtMessage.Text.Trim());
                connection.Open();
                command.ExecuteNonQuery();

            }
        }