Sending bitcoin can be a very straightforward or complex flow in a Bitcoin application. People may be sending bitcoin to a known contact, moving it between their wallets on different devices, or making a purchase through a payment processor.
Let us look at the main transaction options senders need to configure when moving bitcoin:
- Amount — How much to send
- Recipient address — Where to send the bitcoin
- Coin selection — Which coins/inputs to use (optional)
- Fee settings — Prioritize fast confirmation or low cost (optional)
You do not need to follow the order below. Feel free to tailor the configuration’s order for the payment to what best serves your users. For example, you may make users set the amount before they enter the address.
Get the recipient address #
To send a payment on the Bitcoin blockchain, the sender needs to obtain an address from the recipient. Since Bitcoin addresses are long and seemingly random, they are best shared by copying and pasting in plain text, as a payment link, or as a scannable QR Code.
The receiver does this by generating a new address in their wallet application, then sharing it with the sender. If the sender and receiver are physically close to each other, scanning the receiver’s address as a QR Code will be easy. Still, if they are not, they can send the address as text in any regular communication tool like email, SMS, etc.
Inputting an address #
Once you have gotten the address, it’s time to enter the payment details. Bitcoin transactions are irreversible, so both the sender and receiver should take great care in correctly sharing and inputting addresses.
QR Code – Access will need to be granted to your application to enable scanning of QR Codes. Once the camera detects a valid address in the QR Code, it should automatically fill the address field.
Copy Paste – When the sender receives the address or payment link as text, your application can detect a valid address in the clipboard and prompt the sender to press a button to paste it.
- Indicate clearly if the address is valid or not
- Show the full address if possible to help the sender visually verify it is correct
- If space is a constraint, truncate the address in the middle so that both the beginning and end are visible
- Prevent the transaction to be sent if the address is invalid
Inputing an amount #
Unless the sender needs to transfer a specific amount of bitcoin, they should have the ability to switch between other currencies when inputting the amount. It is common practice to provide bitcoin, satoshi, and the sender’s preferred fiat currency as options.
Applications sometimes also allow the sender to select fractions of their total available balance by providing a “max” or “use full balance” button. These fractions can be handy when the sender needs to make transfers from their hot wallet to a more secure hardware wallet.
- Allow senders to switch which denomination they are inputting the amount with
- State the total balance available (subtracting the required fee)
- Allow selecting max amount or fractions for easier fund management
- Payment links and QR Codes can contain an amount. When they do, your application should populate the amount field automatically
- Indicate if an amount entered is more than the available balance
Transaction fee #
The application can automatically estimate a fee and set it for the sender. This would typically prioritize the transaction to be included in a block as soon as possible. Since the fee rate may vary if the network is busy, you can give senders more fine-grained fee controls so they can choose to optimize for faster confirmation or lower fees.
When allowing the sender to set fees, it is essential to communicate the estimated cost in their preferred currency and the estimated time until first confirmation. Be mindful that the way Bitcoin fees get calculated may not map to the sender’s traditional financial experience. If you allow adjustment of fees, consider providing details on how it gets calculated.
Human error with fee selection can lead to costly mistakes, and fee estimations are imperfect. Carefully consider if and how you expose transaction fees to senders.
- Automatically set the fee rate
- Allow sender to choose from presets
- Allow sender to enter a custom fee rate (advanced)
- If the sender does not have advanced knowledge about bitcoin fees but wants control over the fee rate, provide presets to select how urgent the transaction is (e.g. low, medium, high priority)
- When using presets, clearly communicate estimated confirmation time and costs related to each of the fee rate options
- When allowing users to enter their own fee rate, warn the sender if they enter an amount far beyond the recommended fee rate for the next block
Reviewing and approving the payment #
A valid transaction that is broadcasted to the network cannot be reversed, so it is critical that the sender is given a chance to double check the payment details (amount, recipient address, total fee, etc) before submitting the transaction.
If your application allows setting spending limits, and the current transaction exceeds it, make sure they go through some security check (biometric, enter PIN, 2FA password, etc). This technique can also be employed if the transaction is attempting to use the max wallet balance.
- Allow the sender to review payment details like address, amount, and fees and adjust if necessary before submitting the transaction
- Show the amount being sent and the fee information in both bitcoin and the senders preferred currency
Transaction processing and confirmation #
Let us look at how we communicate to the sender about the processing of a transaction after it has been broadcasted. There are three main states that you would want to inform or notify the sender of:
Pending/Unconfirmed – The transaction is successfully in the nodes’ memory pool and is being propagated throughout the network. The fee market can sometimes be volatile, and the “time until the first confirmation” may change from what was estimated when they had initially broadcasted the transaction. While pending, inform the sender of when they can expect the first transaction confirmation.
1 confirmation – The transaction has been selected by miners and included in a block. Since a reorganization can still happen, a transaction with one confirmation can also be considered a pending state by the receiver. This is a good point to notify the sender.
6 confirmations – Commonly regarded as when the final settlement of the payment happens. Merchants, for example, would only be willing to release the product or service at this point.
- Clearly indicate the state of the outgoing transaction
- Show the number of confirmations the transaction has
- Provide information on transaction/block ID for receipt purposes
- Show the transaction as confirmed until it has received at least one confirmation, but preferably six