Producing a proof of work can be a random process with low probability, so that a lot of trial and error is required on average before a valid proof of work is generated. Bitcoin uses the Hashcash proof of work. The Computationally-Difficult Problem. The Bitcoin Network Difficulty Metric. You can use any of these popular Payment Protocol compatible wallets to make secure, successful payments to BitPay merchants. Move Bitcoin or Bitcoin Cash into your spending wallet. For individuals in the United States, the BitPay app provides a simple integration with Coinbase allowing users to buy bitcoin directly from the app. Exchanges and accounts do not send your bitcoin payments immediately, so they are not good for paying BitPay merchants. To use your Bitcoin or Bitcoin Cash, withdraw your Bitcoin or Bitcoin Cash from the exchange to a Payment Protocol compatible wallet before attempting to spend it. Make a payment.