This NIP defines a common API to register push notification tokens into one or more event watch servers, which constantly query several relays to notify users on new events.
The goal is to allow users to choose their event watch servers by simply adding an http address to their account.
After receiving a `token` from the push system (Google Services, Unified Push, Apple Push Notification), clients should upload a list of signed NIP-98 events, one for each account in the device, in a `POST` to `/register` with the following body:
```jsonc
{
"events": [
{
"id": "..",
"pubkey": "...",
"created_at": ...,
"kind": 22242,
"tags":[
[ "relay","<inboxrelay1>" ],
[ "relay","<inboxrelay2>" ],
[ "challenge", "<system>:<token>" ]
],
"content":"",
"sig":"..."
}
]
}
```
where `system` is `google`, `apple` or `unifiedpush`.
Servers will use the `system` information to select where to send new events from the relays marked as such.
The server returns with an array of
```jsonc
[
{
"pubkey": "<pubkey>",
"result": "<added|replaced|error>",
"error": "<message>",
}
]
```
Servers SHOULD accept multiple tokens per pubkey, but may limit the number of them.
Servers SHOULD delete tokens after failure to deliver.
## Sending Events
Servers send new events via the user's preferred system. The event is [NIP-59 GiftWrapped](59.md) to the receiver, but no `p`-tag is added to the wrap event. In that way, the chosen system cannot know which key is receiving this event.
Clients SHOULD try to decrypt the GiftWrap with all logged-in accounts.
