> ## Documentation Index
> Fetch the complete documentation index at: https://docs.invoica.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Supported Chains

> Invoica settles agent payments on Base, SKALE Base, Polygon, Arbitrum, and Solana. Multi-chain by default — every invoice carries its chain context and settles natively on the rail of your choice.

# Supported Chains

Invoica is multi-chain by default. Every invoice carries its `chain` context, and the settlement
watcher polls each chain's native rail to detect incoming USDC transfers and auto-flip invoice
status. No manual settlement, no chain-specific glue code on the caller's side.

<Note>
  **Newest support: SKALE Base** — gasless USDC settlement, sub-second finality. Launched 2026-05-22.
</Note>

## All supported chains

| Chain            | Network ID     | Type          | Status | USDC contract                                  |
| ---------------- | -------------- | ------------- | ------ | ---------------------------------------------- |
| **Base**         | `8453`         | EVM           | Live   | `0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`   |
| **SKALE Base**   | `1187947933`   | EVM (gasless) | Live   | `0x85889c8c714505E0c94b30fcfcF64fE3Ac8FCb20`   |
| **Polygon**      | `137`          | EVM           | Live   | `0x3c499c542cEF5E3811e1192ce70d8cC03d5c3359`   |
| **Arbitrum One** | `42161`        | EVM           | Live   | `0xaf88d065e77c8cC2239327C5EDb3A432268e5831`   |
| **Solana**       | `mainnet-beta` | Solana (SPL)  | Live   | `EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v` |

## How to specify a chain

The `chain` field at the top level of the invoice body determines which rail handles settlement.
The response back-fills `paymentDetails.paymentAddress` (the Invoica seller wallet on that chain)
and `paymentDetails.usdcAddress` (the canonical USDC contract). No separate lookup needed.

```bash theme={null}
curl -sX POST https://api.invoica.ai/v1/invoices \
  -H "x-api-key: $INVOICA_KEY" \
  -H "content-type: application/json" \
  -d '{
    "amount": 0.10,
    "currency": "USDC",
    "customerEmail": "agent@example.com",
    "customerName": "agent-x402",
    "chain": "skale"
  }'
```

Response (201):

```json theme={null}
{
  "success": true,
  "data": {
    "id": "...",
    "invoiceNumber": 1775224117,
    "status": "PENDING",
    "amount": 0.10,
    "currency": "USDC",
    "paymentDetails": {
      "chain": "skale",
      "paymentAddress": "0x3e127c918C83714616CF2416f8A620F1340C19f1",
      "usdcAddress": "0x85889c8c714505E0c94b30fcfcF64fE3Ac8FCb20"
    },
    "createdAt": "..."
  }
}
```

The caller sends USDC to `paymentAddress` on the specified chain. The settlement watcher detects
the transfer (typical latency 15-30 seconds) and flips the invoice to `SETTLED` automatically.
A polling `GET /v1/invoices/{id}` is the recommended client UX.

## Per-chain notes

### Base — `chain: "base"`

The default chain for production agent payments. Coinbase's L2, deep USDC liquidity,
sub-second block times. Use Base for the broadest ecosystem compatibility.

* **Explorer:** [basescan.org](https://basescan.org)
* **Average settlement detection:** 15-25 seconds

### SKALE Base — `chain: "skale"`

EVM-compatible chain running on the SKALE Network's Base subnet. **Zero gas fees** —
the chain pre-allocates compute credits, so USDC transfers cost the sender nothing in
transaction fees. Best fit for high-frequency agent micropayments where per-tx gas would
erode unit economics.

* **Explorer:** [skale-base-explorer.skalenodes.com](https://skale-base-explorer.skalenodes.com)
* **Chain ID:** `1187947933` (`0x46CEA59D`)
* **Faucet (testnet):** Contact SKALE BD for production credits
* **Average settlement detection:** 15-25 seconds

<Tip>
  SKALE Base is the recommended chain for agent-to-agent payments under \$1.00 — gasless
  micropayments without the on-chain fee tail.
</Tip>

### Polygon — `chain: "polygon"`

High-throughput EVM L2. Useful for agent flows that originate or terminate in the broader
Polygon ecosystem (PoS, ZK-EVM).

* **Explorer:** [polygonscan.com](https://polygonscan.com)
* **Average settlement detection:** 20-40 seconds (slower block times)

### Arbitrum One — `chain: "arbitrum"`

Arbitrum's optimistic rollup. Among the lowest fees of Ethereum L2s for high-frequency
micropayments.

* **Explorer:** [arbiscan.io](https://arbiscan.io)
* **Average settlement detection:** 15-25 seconds

### Solana — `chain: "solana"`

Native Solana settlement via the [PayAI x402 facilitator](https://payai.network).
SPL Token transfers carry a memo-based invoice reference; settlement detection uses
signature polling on the seller wallet.

* **Explorer:** [solscan.io](https://solscan.io)
* **USDC mint:** `EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v`
* **Token program:** `TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA`
* **Average settlement detection:** depends on RPC tier (\~30 seconds with authed RPC)

<Warning>
  Solana detection requires an authenticated RPC endpoint (public mainnet RPC is heavily
  rate-limited). Set `SOLANA_RPC_URL` to your Helius / QuickNode / Triton endpoint when
  self-hosting the settlement watcher.
</Warning>

## Settlement flow (all chains)

The lifecycle is identical regardless of chain:

```
1. POST /v1/invoices       → invoice created, status=PENDING
2. <caller transfers USDC> → on the chain specified, to paymentAddress
3. <watcher detects>       → typically 15-30s after on-chain confirmation
4. Auto-flip               → status=SETTLED, paymentDetails enriched with
                              txHash + settlementBlockNumber +
                              settlementSource='evm-detector' (or 'solana-detector')
5. GET /v1/invoices/{id}   → client polls; webhook 'invoice.settled' also fires
```

The client never needs to PATCH the invoice status. Settlement is a system-detected event.

## On-chain audit trail

Every settled invoice produces a **DRS receipt** anchored on Base (mainnet for production
invoices; Base Sepolia for v0.1 PACT Mandate API). The receipt hashes the mandate, settlement
details, tax line, and payout breakdown into a single on-chain event that's verifiable years
later via the chain's explorer.

See [DRS receipts](/concepts/pact) for the protocol details.

## Adding a new chain

We add chains based on real customer pull. Two paths:

1. **EVM chain** — if the chain has Coinbase CDP / Polymer / similar x402 facilitator support
   AND a USDC contract address, integration is typically 2-5 business days.
2. **Non-EVM chain** — requires a custom detector module. Solana took \~1 week. Other ecosystems
   (Aptos, Sui, Tron) would be similar.

To request a chain: email [support@invoica.ai](mailto:support@invoica.ai?subject=Chain%20support%20request) with your use case.

***

**Related:** [x402 Protocol](/concepts/x402-protocol) · [Invoice Middleware](/concepts/invoice-middleware) · [PACT](/concepts/pact)