If you believe that the webhook had been created. In https://my-domain/apps/app-name/uninstall.php
put these line of code
$webhook = file_get_contents('php://input');
$webhook = json_decode($webhook, TRUE);
$newFileName = "something.txt";
file_put_contents($newFileName, $webhook);
It will catch the json shopify send when you uninstall your apps and put into file something.txt after that get the info your use to store. Json usually look like
{
"id": 690933842,
"name": "Super Toys",
"email": "[email protected]",
"domain": "super.myshopify.com",
"province": "Tennessee",
"country": "US",
"address1": "190 MacLaren Street",
"zip": "37178",
"city": "Houston",
"source": null,
"phone": "3213213210",
"latitude": null,
"longitude": null,
"primary_locale": "en",
"address2": null,
"created_at": null,
"updated_at": null,
"country_code": "US",
"country_name": "United States",
"currency": "USD",
"customer_email": "[email protected]",
"timezone": "(GMT-05:00) Eastern Time (US & Canada)",
"iana_timezone": null,
"shop_owner": "Steve Jobs",
"money_format": "$",
"money_with_currency_format": "$ USD",
"weight_unit": "kg",
"province_code": "TN",
"taxes_included": null,
"tax_shipping": null,
"county_taxes": null,
"plan_display_name": "Shopify Plus",
"plan_name": "enterprise",
"has_discounts": true,
"has_gift_cards": true,
"myshopify_domain": null,
"google_apps_domain": null,
"google_apps_login_enabled": null,
"money_in_emails_format": "$",
"money_with_currency_in_emails_format": "$ USD",
"eligible_for_payments": true,
"requires_extra_payments_agreement": false,
"password_enabled": null,
"has_storefront": true,
"eligible_for_card_reader_giveaway": false,
"finances": true,
"primary_location_id": 905684977,
"checkout_api_supported": true,
"multi_location_enabled": false,
"setup_required": false,
"force_ssl": false,
"pre_launch_enabled": false,
"enabled_presentment_currencies": [
"USD"
]
}