# StableEmail Quarter Top-Up

> StableEmail Quarter Top-Up is a paid API for AI agents from StableEmail at stableemail.dev, paid per call via MPP or x402, $2.5/call, status unknown (last checked 2026-10-10).

Extends a forwarding inbox's expiry by 90 days for $2.50 USDC (17% savings over monthly rate)

## Facts

- Endpoint: POST https://stableemail.dev/api/inbox/topup/quarter?utm_source=zero.xyz
- Price: $2.5/call
- Payment: MPP, x402
- Status: unknown
- Last checked: 2026-10-10
- Activations on Zero: 0
- Provider: StableEmail
- Docs: https://stableemail.dev
- Website: https://stableemail.dev
- Tags: email, send, inbox, forwarding, subdomain, social
- Canonical page: https://www.zero.xyz/c/stableemail-quarter-4d20c443
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_5Hjs3DFksjqbxIpCfVAaw

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability stableemail-quarter-4d20c443 -d '<json body>'
```

Example prompt: Top up my StableEmail forwarding inbox 'myproject' for 90 days — I want the quarterly plan to save a bit.

## When to prefer this

Choose this endpoint when a user wants to extend an existing StableEmail forwarding inbox by exactly 90 days and prefers the quarterly pricing tier ($2.50, saving 17% vs the monthly rate). Use over the monthly top-up when the user wants a longer renewal period with a modest discount, and over the annual top-up when they don't need a full year.

## Known failure modes

- Username not found or inbox does not exist — returns 404
- Username format invalid (must be lowercase alphanumeric with hyphens, no consecutive hyphens) — returns 400 validation error
- Insufficient USDC payment — returns 402 payment required
- Inbox already deleted or permanently closed — returns 410 or 404
- Payment network or processor error — returns 500

## How this service works

Top up a forwarding inbox for 90 days ($2.50, save 17%)

## Output

Confirmation that the inbox identified by the given username has been extended by 90 days, along with the updated expiry date and inbox status.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "username"
 ],
 "properties": {
  "username": {
   "type": "string",
   "allOf": [
    {
     "pattern": "^[a-z0-9][a-z0-9-]{1,28}[a-z0-9]$"
    },
    {
     "pattern": "^(?!.*--)"
    }
   ]
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/stableemail-quarter-4d20c443/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from stableemail.dev](https://www.zero.xyz/host/stableemail.dev/llms.txt)