Xcode Apple審査のリジェクト（課金のレシート検証？）修正について

こんにちは。
Xcodeでの課金部分でAppleの審査が通らず困っております。ご助言いただければ幸いです。
いずれもソフトは最新バージョンです。
以下引用の通りAppleより2度リジェクトされております。
なんとなくレシートがSandbox用なのにProductサーバーに送っちゃってるからどこかで条件分岐しろみたいなことだと理解しているんですが、コードのどこでどう分岐してどう記述すれば良いのかわかりません。
そもそも自身の環境では、SandboxでもTestFlight環境でもうまく動作するため、よくわからずにいます。
ネット上では課金部分のコードサンプルが少なく、ここ数日困っています。
よろしくお願いいたします。

We found that your in-app purchase products exhibited one or more bugs when reviewed on iPad running iOS 14.0 on Wi-Fi.

We were still unable to purchase your in-app purchase products because nothing occurred after tapped action buttons.

Next Steps

When validating receipts on your server, your server needs to be able to handle a production-signed app getting its receipts from Apple’s test environment. The recommended approach is for your production server to always validate receipts against the production App Store first. If validation fails with the error code "Sandbox receipt used in production," you should validate against the test environment instead.

Swift
1import UIKit
2import SwiftyStoreKit
3import Firebase
4
5class BillingViewController: UIViewController {
6    
7    @IBOutlet weak var pointLabel: UILabel!
8    
9    var userPoint = Int()
10    let userid = Auth.auth().currentUser?.uid
11    let indicator = UIActivityIndicatorView()
12    
13    @IBOutlet weak var buy500PointButton: UIButton!
14    @IBOutlet weak var buy1000PointButton: UIButton!
15    @IBOutlet weak var buy1500PointButton: UIButton!
16    @IBOutlet weak var buy2000PointButton: UIButton!
17    
18    override func viewDidLoad() {
19        super.viewDidLoad()
20
21        
22        // Do any additional setup after loading the view.
23    }
24    
25    
26    
27    
28    func purchase(PRODUCT_ID:String,POINT:Int){
29        
30        SwiftyStoreKit.purchaseProduct(PRODUCT_ID) { (result) in
31            
32            self.indicator.stopAnimating()
33            
34            //            ボタンを元の状態に戻す
35            self.changeButton()
36            
37            switch result{
38            case .success(_):
39                //                購入成功
40                //                購入検証
41                self.verifyPurchase(PRODUCT_ID: PRODUCT_ID,POINT: POINT)
42
43                break
44                
45            case .error(let error):
46                //                購入失敗
47                print(error)
48                
49                break
50            }
51        }
52    }
53    
54    
55    func verifyPurchase(PRODUCT_ID:String,POINT:Int){
56        let appleValidator = AppleReceiptValidator(service: .production, sharedSecret: "aaaaaaaaaaaaaaaaaaaaa")
57        SwiftyStoreKit.verifyReceipt(using: appleValidator) { (result) in
58            switch result{
59            case .success(let receipt):
60                let purchaseResult = SwiftyStoreKit.verifyPurchase(productId: PRODUCT_ID, inReceipt: receipt)
61                
62                switch purchaseResult {
63                    //                        リストア成功
64                //                        購入があったときの処理を記載
65                
66                case .purchased:
67                    self.updateUserPoint(point: POINT)
68                    break
69                case .notPurchased:
70                    
71                    break
72                }
73                
74                break
75            case .error(error: let error):
76                print(error)
77                
78            }
79            
80            
81        }
82        
83    }
84    
85    
86    
87    @IBAction func buy500PointAction(_ sender: Any) {
88        buy500PointButton.isEnabled = false
89        buy500PointButton.backgroundColor = .gray
90        buy500PointButton.alpha = 0.5
91        
92        purchase(PRODUCT_ID: "500point",POINT: 500)
93        
94    }
95    
96    @IBAction func buy1000PointAction(_ sender: Any) {
97        buy1000PointButton.isEnabled = false
98        buy1000PointButton.backgroundColor = .gray
99        buy1000PointButton.alpha = 0.5
100        purchase(PRODUCT_ID: "1000point",POINT: 1000)
101        
102    }
103    
104    @IBAction func buy1500PointAction(_ sender: Any) {
105        buy1500PointButton.isEnabled = false
106        buy1500PointButton.backgroundColor = .gray
107        buy1500PointButton.alpha = 0.5
108        purchase(PRODUCT_ID: "1500point",POINT: 1500)
109        
110    }
111    
112    
113    @IBAction func buy2000PointAction(_ sender: Any) {
114        buy2000PointButton.isEnabled = false
115        buy2000PointButton.backgroundColor = .gray
116        buy2000PointButton.alpha = 0.5
117        purchase(PRODUCT_ID: "2000point",POINT: 2000)
118        
119    }
120    
121    
122    
123   
124    
125    func changeButton(){
126        buy500PointButton.isEnabled = true
127        buy500PointButton.backgroundColor = .systemPink
128        buy500PointButton.alpha = 1
129        
130        buy1000PointButton.isEnabled = true
131        buy1000PointButton.backgroundColor = .systemPink
132        buy1000PointButton.alpha = 1
133        
134        buy1500PointButton.isEnabled = true
135        buy1500PointButton.backgroundColor = .systemPink
136        buy1500PointButton.alpha = 1
137        
138        buy2000PointButton.isEnabled = true
139        buy2000PointButton.backgroundColor = .systemPink
140        buy2000PointButton.alpha = 1
141        
142    }
143    
144    
145    
146}
147