You can check your Apple App Store order number through the payment receipt sent to your Apple account email or through the following path:

[Method 1 to check App Store payment history on iOS/iPadOS mobile devices]
Launch App Store → Tap Today profile → Tap your Apple ID and enter password → Purchase History → Tap Change Filter and set filters → Set date range to "Last 90 days", cost to "Paid", type to "In-App Purchases" → Tap "Total" in purchase history to view order details

[Method 2 to check App Store payment history on iOS/iPadOS mobile devices]
Settings → Tap Apple ID, iCloud, Media & Purchases at top → Media & Purchases → View Account → Purchase History → Tap Change Filter and set filters → Set date range to "Last 90 days", cost to "Paid", type to "In-App Purchases" → Tap "Total" in purchase history to view order details