# NIP-89

## payto: Payment Targets

`draft` `optional` `author:atxmj`

This NIP standardizes the approach to payment and tip invocations from user profiles, posts, chats, and elsewhere using the [RFC-8905 (payto:) URI scheme](https://www.rfc-editor.org/rfc/rfc8905.html) standard for "payment targets".

### payto: event broadcasting

Clients *may* allow users to specify a list (one or many) of "payment targets" as specified in the [RFC-8905 (payto:) URI scheme](https://www.rfc-editor.org/rfc/rfc8905.html) standard, each consisting of a pair of values, `payment_target_type` and `authority` (to be labeled as preferred by the client), in order to generate an event of kind `0` (`set_metadata`) specifying "payment targets" that *may* be used for payment or tip invocation from a user's profile, posts, chats, or elsewhere.

The client *may* allow the user to input and perform validation on the `payment_target_type` and `authority` fields (labeled as preferred by the client) as they see fit.

### Example of broadcasting a "payto" event

The client allows the user to add multiple pairs of "payment network" and "address" values to a list of "payment options" in their profile.

The client performs validation on the inputs and warns the user that the "payment network" for the third "payment option" with value `unknowntype` is [not recognized](#recommended-payment-target-types), but allows them to submit it regardless.

The client then broadcasts an event such as

```json
{
  "pubkey": "afc93622eb4d79c0fb75e56e0c14553f7214b0a466abeba14cb38968c6755e6a",
  "kind": 0,
  "content": "{\"payto\": [{\"payment_target_type\": \"bitcoin\", \"authority\": \"bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k\"}, {\"payment_target_type\": \"nano\", \"authority\": \"nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c\"}, {\"payment_target_type\": \"unknowntype\", \"authority\": \"l7tbta5b9xze6ckkfc99uohzxd009b0r\"}]}"
  ...
}
```

#### Example of steps taken by the client on input

- allow the user to specify a list of `payment_target_type` and `authority` value pairs (labeled as preferred by the client) of their choice
- for each pair of `payment_target_type` and `authority` values specified by the user
    - *optionally* do some minimal validation on those fields in a generalized way that applies to any payment network
    - *optionally* warn users if a specifid `payment_target_type` is not [*recognized*](#recommended-payment-target-types) by the client
- broadcast the event in the format specified above

### Recommended Payment Target Types

This is a list of recommended payment target types for clients to recognize and store icons and stylization configurations for.

| Payment Target Type | Long Stylization  | Short Stylization | Symbol | References |
| :------------------ | :---------------- | :---------------- | :----- | :--------- |
| bitcoin             | Bitcoin           | BTC               | ₿      | https://bitcoin.design/ |
| lightning           | Lightning Network | LBTC              | —      | https://github.com/shocknet/bitcoin-lightning-logo |
| cashme              | Cash App          | Cash App          | –      | https://cash.app/press |
| nano                | Nano              | XNO               | Ӿ      | https://nano.org/en/currency |

### payto: event observation

On observation of events of kind `0` (`set_metadata`), the event *may* specify the key `"payto"` with a value consisting of a list (one or many) of "payment target" values, each specified as a pair of values `payment_target_type` and `authority` as specified in the [RFC-8905 (payto:) URI scheme](https://www.rfc-editor.org/rfc/rfc8905.html) for payment targets.

For each pair of values in the `payto` list, the client *should* assemble a full `payto://` deep link URI and render it as a button or link in the user's profile, posts, chats, or elsewhere, in the format of `payto://<payment_target_type>/<authority>`. 

The client *should* store a map of [recognized payment target types](#recommended-payment-target-types) along with a corresponding icon & stylization configuration (to be defined by the client).

For ***recognized*** `payment_target_type` values, the client *should* render a button or link using the associated icon & stylization. 

For ***unrecognized*** `payment_target_type` values, the client *may* chose to either ignore them or use a generic stylization, perhaps using the `payment_target_type` value directly for the button or link.

If a user has specified multiple payment targets, the client *may* choose to render only the first one, render multiple buttons or links, or render a dropdown to select the payment target of choice.

### Example of observing a "payto" event

If a client sees an event like this:

```json
{
  "pubkey": "afc93622eb4d79c0fb75e56e0c14553f7214b0a466abeba14cb38968c6755e6a",
  "kind": 0,
  "content": "{\"payto\": [{\"payment_target_type\": \"bitcoin\", \"authority\": \"bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k\"}, {\"payment_target_type\": \"nano\", \"authority\": \"nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c\"}, {\"payment_target_type\": \"unknowntype\", \"authority\": \"l7tbta5b9xze6ckkfc99uohzxd009b0r\"}]}"
  ...
}
```

for each payment target it will assemble a deep link payment invocation URI, as

`payto://bitcoin/bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k` (*recognized*)
`payto://nano/nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c` (*recognized*)
`payto://unknowntype/l7tbta5b9xze6ckkfc99uohzxd009b0r` (*unrecognized*)

The client chooses to ignore the third *unrecognized* `payment_target_type`, and only embeds the first two payment target deep links in the user's profile, posts, chats, or elsewhere as buttons, links, or a dropdown selector using the corresponding icons & stylizations for the [*recognized* payment target types](#recommended-payment-target-types).

*Optionally*, the client may have chosen to render the third payment target using the text `unknowntype` rather than ignoring it.

#### Example of steps taken by the client on observation

- for each pair of `payment_target_type` and `authority` values in the `payto` list
    - *optionally* do some minimal validation on those fields in a generalized way that applies to any payment network, and filter out invalid pairs
    - *optionally* filter out any pairs with an [*unrecognized*](#recommended-payment-target-types) `payment_target_type`
    - assemble a full `payto://` deep link URI in the format `payto://<payment_target_type>/<authority>`
    - render a button, link, or dropdown in user profiles, posts, chats, and elsewhere using the assembled deep links and the corresponding icons & stylization configurations for *recognized* `payment_target_type` values