Start here · primary technical demonstration
Judge Demo: OpenTab on Stellar Testnet
Explore our working demonstration of offline family payments. Senders fund a family wallet, family members authorize payments without internet, and merchants settle confirmed transactions on Stellar Testnet.
- For judges: this Demo Mode is the real, working app. Use the Sender, Family and Shop tabs above.
- Stellar Testnet, not Mainnet. Every confirmation is a real Testnet transaction you can open on Stellar Expert.
- No real money. Payments use the OTUSD test token, which has no monetary value.
- No access code needed: anyone can add funds to and pair a phone with demo Family #7 (Sender), approve on the Family wallet and settle at the Shop. Revoking devices and creating families are turned off.
Switch to Product Mode to explore how OpenTab would look for everyday families and merchants. It is a read-only preview of the consumer interface, showing the real demo Family #7 data where supported; payments still run here in Demo Mode.
Pay at the corner shop with a phone that has no data.
A relative abroad funds a family balance on Stellar. At a participating shop, the family member approves the purchase on their phone while offline; the connected shop submits that approval and is paid by a smart contract.
The payment flow
- 1Sender abroad, online
Funds the shared family balance - 2Shop online
Shows an invoice QR: local price + exact charge - 3Family phone OFFLINE
Checks it and signs that exact purchase - 4Shop online
Scans the approval and submits it - 5Stellar FamilyVault contract
Verifies and pays the shop, once
The shop sees Payment confirmed only after the Stellar transaction succeeds. A second attempt with the same approval is refused by the contract.
1 · Sender
See Family #7's balance, add funds, pair a family member. Public.
2 · Family phone
Set up the device, then Scan to Pay: review and approve offline, show the signed QR. Public.
3 · Shop
Select a product, show the invoice, scan the approval, settle on Stellar. Public.
Live activity · Family #7
Confirmed payments read from the FamilyVault contract on Stellar Testnet (about the last day). Updates every 20 seconds while this page is open.
No confirmed payments in the recent window.
How an offline approval can be trusted
- The phone creates an Ed25519 key. Only the public key is shared; the sender registers it on chain.
- Approving builds a fixed 340-byte message: Testnet ID, this contract, the token, family, shop, terminal, a random invoice ID, the exact amount, a hash of the local price and rate, and an expiry. The phone signs it locally, with no network.
- The contract rebuilds the same bytes from its own state, verifies the signature, refuses used or expired invoices, checks the balance, and transfers the tokens in one atomic transaction.
- Change any field (amount, shop, network) and the signature no longer verifies.
What works today vs. what is next
Connected shop, offline customer
One shared family balance spendable at any participating shop with internet. This is what the demo shows.
Both offline
Funds reserved on chain for one named shop; the shop accepts running-total tickets offline and settles later. Contract written and unit-tested (24 tests); not deployed and not part of this demo.
Verified on Stellar Testnet
- FamilyVault
CAUCH3MNJGIYDLOY3OB3YCKRCBWWY3J3HZB5QCHPJXUWXBMK5IABYLGW- Asset
- OpenTab Demo USD (OTUSD): Testnet only, no value, not USDC
- Asset contract
CC6JPD3NL3ZJMWT2JG246ISOG5QB2N72BG77KPVC3OCDEYUHK2TEPL73- Issuer
GCZDLLF3OYZVD5HDKN3DRP475ICCKMRN6Q3PHNMTILABZWSGWPS5RCAY- Tienda Rosa
GCDSS6VQP6GGTV6K2J6FMG2TQN2G2EG37TSQ5UYQK547ODDYGNPPRWN4- Farmacia Luz
GBIIBDC4PM237AP57I42FO4GGKDUC53ZAQXIOOALVFBNCOLDULKJGEAI
- First signed merchant payment (CLI)
MXN 100.00 → 5.4288817 OTUSD to Tienda Rosa
Open on Stellar Expert ↗0b8d72ed8e… - Same family balance, second shop
MXN 50.00 → 2.7144409 OTUSD to Farmacia Luz
Open on Stellar Expert ↗009cc536cc… - Payment made through the app UI (recipient offline while signing)
MXN 20.00 → 1.0857764 OTUSD; replay then rejected
Open on Stellar Expert ↗e42405a85a… - FamilyVault deployment
Contract deployed to Stellar Testnet
Open on Stellar Expert ↗86f91a10b0…
Demo preflight (read-only, spends nothing)
Running checks…
Exchange rates are illustrative, not live quotes. No bank payouts exist. Unaudited prototype; not a financial service.