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If you have received a payment to some address, which is not listed in your wallet, but was generated from your XPub — don't worry, it's not lost and can be recovered as follows:

1. install Electrum (tested on version 2.7.12)
2. in Electrum, restore wallet with the inaccessible funds from its BIP32 Passphrase (also called Seed, 13 words)
3. in the restored wallet, switch to Console tab, paste getmasterprivate(), hit enter
4. visit bip32.org
5. select "Derive From: BIP32 Key"
6. paste xprv… from Electrum Console into the "BIP32 Extended Key" field
7. select "Derivation Path: Custom"
8. paste m/0/n (or whatever is your gateway's address_derivation_scheme) into the "Custom Path" field, where n is the order's keychain_id
9. ensure that generated value in "Address" field is equal to the order's address
10. copy value from the "Private Key (WIF)" field
11. import the obtained keys into a new wallet in Electrum: "File -> New/Restore -> Standard wallet -> Use public or private keys"
12. paste one or more "Private Key (WIF)" values, one per line
13. on the next step, addresses should appear on "Addresses" tab with the actual balances, ready to be spent

If this did help when all hope was lost, thanks are welcome to 1HoMxr9eDShApAHJnbsF1rTaTbcXehUpQX :)