Lynx.

Lynx is a sleek and elegant self-custody crypto wallet with a very secure payment feature which allows a two-party (merchant and customer) integrity check of the transaction at all times.

Non-intuitiveness : In order to maximize efficiency, Lynx is NOT designed for immediate, off-the-shelf use, you need to read the manual first to be able to use it (it’s not long, don’t worry) : https://lynx.tf

With the payment feature, the merchant is able to verify the integrity of the payment details(the price, the blockchain used,…) settled by the customer, on his own iPhone without any chance of external tampering as well as making offline signature verification.

On the other hand, the customer only signs for the specific amount of funds explicitly asked by the merchant and not more, the manual explains this feature in detail.

Finally, before processing the transaction, the merchant will recheck the integrity of the transaction : If there is any error in the receiving address or the amount, the transaction will be immediately cancelled before being processed. As long as you use the payment feature, it is impossible for erroneous transactions to be processed, and thus for funds to be lost.

Bitcoin is available for all users, while subscribers get access to Ethereum, Polygon and USDC on Polygon.

By using Lynx, you agree to its Terms of service (https://madewithlove.tf/privacy.html)

One last thing : When you go out to have a walk downtown, you never happen to hold 5000 $ in cash in your pocket because it's both very useless and very dangerous. Lynx (like EVERY mobile self-custody crypto wallet) is not designed to hold large amounts of money, you should never have more than around 2000 $ at any given time (more or less depending on your cost of living) except if you already planned to spend the money soon. If you need to store large amounts of money, you have to use a hardware wallet like ledger.com or trezor.io, or deposit funds in an exchange like Binance. Lynx is for payments not store of value.