Detecting Promo code in IAP receipt validateion - ios

Question

In-App Purchase is successfully added in Application
IAP is currently in development mode and I put the IAP Receipt Validation on server end and it's working fine.
Now I want to integrate Promo Codes for IAP. but they can be generated upon approval from Apple (IAP Review)
Question: How would I detect that an Promo Code has been used against a transaction as the receipt validation response coming from Apple Server doesn't contain transaction amount or any promo code field
example:
{
"receipt": {
"receipt_type": "ProductionSandbox",
"adam_id": 0,
"app_item_id": 0,
"bundle_id": "com.myApp",
"application_version": "14.06",
"download_id": 0,
"version_external_identifier": 0,
"receipt_creation_date": "2018-09-05 05:18:33 Etc/GMT",
"receipt_creation_date_ms": "1536124713000",
"receipt_creation_date_pst": "2018-09-04 22:18:33 America/Los_Angeles",
"request_date": "2018-09-25 04:53:09 Etc/GMT",
"request_date_ms": "1537851189557",
"request_date_pst": "2018-09-24 21:53:09 America/Los_Angeles",
"original_purchase_date": "2013-08-01 07:00:00 Etc/GMT",
"original_purchase_date_ms": "1375340400000",
"original_purchase_date_pst": "2013-08-01 00:00:00 America/Los_Angeles",
"original_application_version": "1.0",
"in_app": [
{
"quantity": "1",
"product_id": "com.myApp.testpack",
"transaction_id": "1000000439689939",
"original_transaction_id": "1000000439689939",
"purchase_date": "2018-09-05 05:03:52 Etc/GMT",
"purchase_date_ms": "1536123832000",
"purchase_date_pst": "2018-09-04 22:03:52 America/Los_Angeles",
"original_purchase_date": "2018-09-05 05:03:52 Etc/GMT",
"original_purchase_date_ms": "1536123832000",
"original_purchase_date_pst": "2018-09-04 22:03:52 America/Los_Angeles",
"is_trial_period": "false"
},
{
"quantity": "1",
"product_id": "com.myApp.testpack",
"transaction_id": "1000000439690499",
"original_transaction_id": "1000000439690499",
"purchase_date": "2018-09-05 05:09:38 Etc/GMT",
"purchase_date_ms": "1536124178000",
"purchase_date_pst": "2018-09-04 22:09:38 America/Los_Angeles",
"original_purchase_date": "2018-09-05 05:09:38 Etc/GMT",
"original_purchase_date_ms": "1536124178000",
"original_purchase_date_pst": "2018-09-04 22:09:38 America/Los_Angeles",
"is_trial_period": "false"
},
{
"quantity": "1",
"product_id": "com.myApp.testpack",
"transaction_id": "1000000439692512",
"original_transaction_id": "1000000439692512",
"purchase_date": "2018-09-05 05:18:01 Etc/GMT",
"purchase_date_ms": "1536124681000",
"purchase_date_pst": "2018-09-04 22:18:01 America/Los_Angeles",
"original_purchase_date": "2018-09-05 05:18:01 Etc/GMT",
"original_purchase_date_ms": "1536124681000",
"original_purchase_date_pst": "2018-09-04 22:18:01 America/Los_Angeles",
"is_trial_period": "false"
}
]
},
"status": 0,
"environment": "Sandbox"
}
I just want to store the coupon code which was used during the transaction in my database for some analysis.

Answer 1

#Paulw11 mentioned in comments there is no way of knowing from the receipt or within the app itself.
I began searching for ways to fetch details from the App Analytics and found that Apple provides Reporter which can let us download the reports from the App Analytics. This is based in Java. but people have port this to another language also.
Useful Libraries:
PHP
https://github.com/fedoco/itc-reporter
Python
https://github.com/fedoco/itc-reporter