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+# NIP-A3
+
+## payto: Payment Targets (RFC-8905)
+
+### Event Kind
+
+This NIP defines `kind:10133` for payment target events. This kind is **replaceable**.
+
+`optional` `author:atxmj`
+
+This NIP standardizes payment and tip invocations using the [RFC-8905 (payto:) URI scheme](https://www.rfc-editor.org/rfc/rfc8905.html) for payment targets.
+
+### Broadcasting
+
+Clients *may* allow users to specify payment targets consisting of `type` and `authority` values to generate a kind `10133` event with `payto` tags for payment or tip invocations.
+
+**Client Implementation:**
+1. Allow users to input `type` and `authority` pairs
+2. Validate inputs according to the rules below
+3. Optionally warn users if a `type` is not recognized (but allow submission)
+4. Broadcast the event with `payto` tags
+
+#### Tag Format
+
+Payment targets are specified using `payto` tags with the following structure:
+
+```text
+["payto", "<type>", "<authority>", "<optional_extra_1>", "<optional_extra_2>", ...]
+```
+
+Where:
+- The first element is always the literal string `"payto"`
+- The second element is the payment `type` (e.g., `"bitcoin"`, `"lightning"`)
+- The third element is the `authority` (e.g., address, username)
+- Additional elements are optional and reserved for future RFC-8905 features
+
+Clients **must** understand elements 0–2; they **may ignore** any additional elements for forward compatibility.
+
+#### Validation
+
+- `type`: Lowercase letters (a-z), digits (0-9), and hyphens (-). Types are case-insensitive; normalize to lowercase.
+- `authority`: URL-safe; URL-encode special characters. Format depends on the payment system.
+- Clients may perform additional payment-system-specific validation for recognized types.
+
+### Broadcasting Example
+
+```json
+{
+  "pubkey": "afc93622eb4d79c0fb75e56e0c14553f7214b0a466abeba14cb38968c6755e6a",
+  "kind": 10133,
+  "content": "",
+  "tags": [
+    ["payto", "bitcoin", "bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k"],
+    ["payto", "nano", "nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c"],
+    ["payto", "unknowntype", "l7tbta5b9xze6ckkfc99uohzxd009b0r"]
+  ],
+  ...
+}
+```
+
+### Recommended Payment Target Types
+
+| Payment Target Type | Long Stylization  | Short Stylization | Symbol | References |
+| :------------------ | :---------------- | :---------------- | :----- | :--------- |
+| bitcoin             | Bitcoin           | BTC               | ₿      | https://bitcoin.design/ |
+| cashme              | Cash App          | Cash App          | $,£    | https://cash.app/press |
+| ethereum            | Ethereum          | ETH               | Ξ      | https://ethereum.org/assets/#brand |
+| lightning           | Lightning Network | LBTC              | 丰     | https://github.com/shocknet/bitcoin-lightning-logo |
+| monero              | Monero            | XMR               | ɱ      | https://www.getmonero.org/press-kit/ |
+| nano                | Nano              | XNO               | Ӿ      | https://nano.org/en/currency |
+| revolut             | Revolut           | Revolut           | N/A    | https://revolut.me |
+| venmo               | Venmo             | Venmo             | $      | https://venmo.com/pay |
+
+### Observation
+
+For each `payto` tag in kind `10133` events, clients *should* assemble a `payto://<type>/<authority>` URI and render it as a button or link.
+
+**Client Implementation:**
+1. Parse each `payto` tag from the event
+2. Optionally validate `type` and `authority` fields and filter invalid tags
+3. Assemble full `payto://<type>/<authority>` URIs
+4. For **recognized** types, render with associated icons and stylization from the table above
+5. For **unrecognized** types, either ignore or use generic stylization
+6. If multiple targets exist, render the first one, all of them, or a dropdown selector
+
+### Observation Example
+
+```json
+{
+  "pubkey": "afc93622eb4d79c0fb75e56e0c14553f7214b0a466abeba14cb38968c6755e6a",
+  "kind": 10133,
+  "content": "",
+  "tags": [
+    ["payto", "bitcoin", "bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k"],
+    ["payto", "nano", "nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c"],
+    ["payto", "unknowntype", "l7tbta5b9xze6ckkfc99uohzxd009b0r"]
+  ],
+  ...
+}
+```
+
+Assembled URIs:
+- `payto://bitcoin/bc1qxq66e0t8d7ugdecwnmv58e90tpry23nc84pg9k` (recognized)
+- `payto://nano/nano_1dctqbmqxfppo9pswbm6kg9d4s4mbraqn8i4m7ob9gnzz91aurmuho48jx3c` (recognized)
+- `payto://unknowntype/l7tbta5b9xze6ckkfc99uohzxd009b0r` (unrecognized)
+
+## Implementation Notes
+
+### Integration with NIP-57 Zaps
+
+Clients may use `payto` lightning entries as an alternative or complement to `lud16` for zap functionality. The `authority` field should contain a Lightning address (e.g., `user@wallet.example.com`) or LNURL.
+
+Example:
+
+```json
+[
+  {
+    "kind": 0,
+    "content": "{\"lud16\":\"user@wallet.example.com\"}",
+    "pubkey": "..."
+  },
+  {
+    "kind": 10133,
+    "content": "",
+    "tags": [
+      ["payto", "lightning", "user@wallet.example.com"],
+      ["payto", "bitcoin", "bc1q..."]
+    ],
+    "pubkey": "..."
+  }
+]
+```
\ No newline at end of file
diff --git a/README.md b/README.md
index ccae3aa006..d463ddcb99 100644
--- a/README.md
+++ b/README.md
@@ -108,6 +108,7 @@ They exist to document what may be implemented by [Nostr](https://github.com/nos
 - [NIP-C0: Code Snippets](C0.md)
 - [NIP-C7: Chats](C7.md)
 - [NIP-EE: E2EE Messaging using MLS Protocol](EE.md)
+- [NIP-A3: payto: Payment Targets (RFC-8905)](A3.md)
 
 ## Event Kinds
 | kind          | description                     | NIP                                    |
@@ -211,6 +212,7 @@ They exist to document what may be implemented by [Nostr](https://github.com/nos
 | `10051`       | KeyPackage Relays List          | [EE](EE.md)                            |
 | `10063`       | User server list                | [Blossom][blossom]                     |
 | `10096`       | File storage server list        | [96](96.md) (deprecated)               |
+| `10133`       | Payment Targets                 | [A3](A3.md)                            |
 | `10166`       | Relay Monitor Announcement      | [66](66.md)                            |
 | `10312`       | Room Presence                   | [53](53.md)                            |
 | `10377`       | Proxy Announcement              | [Nostr Epoxy][nostr-epoxy]             |