Build Close-Position Payload

// Replace `<action>` with the action of THIS page (e.g. create-account, deposit, …)
const endpoint = 'api/2/perp/payloads/<action>';
const timestamp = Date.now();
const signature = await wallet.signMessage(`${endpoint}-${timestamp}`);

await fetch(`https://api.mobula.io/${endpoint}`, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    timestamp,
    signature,
    // ...action-specific fields below
  }),
});

import { ethers } from 'ethers';

// 1. Auth-sign + fetch the close-position payload
const endpoint = 'api/2/perp/payloads/close-position';
const ts = Date.now();
const authSig = await wallet.signMessage(`${endpoint}-${ts}`);

const { data } = await fetch(`https://api.mobula.io/${endpoint}`, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    timestamp: ts,
    signature: authSig,
    dex: 'gains',                    // or 'lighter'
    chainId: 'evm:42161',            // or 'lighter:301'
    marketId: 'gains-btc-usd',
    positionId: '12345',             // Gains only — Gains trade index
    closePercentage: 50,             // close 50%; or use amountRaw
  }),
}).then(r => r.json());

// 2. Branch on transport
let signedTx;
const finalPayloadStr = data.payloadStr; // close-position never mutates the envelope

if (data.transport === 'evm-tx') {
  // Gains: sign the single EVM tx and pass as top-level signedTx.
  // Read nonce / feeData from a real chain RPC — NOT an embedded-wallet
  // provider, which can return stale or default-to-0 nonce.
  const txData = JSON.parse(data.payloadStr).payload.data;
  const provider = new ethers.JsonRpcProvider(rpcUrlFor(txData.chainId));
  const [nonce, feeData] = await Promise.all([
    provider.getTransactionCount(wallet.address, 'pending'),
    provider.getFeeData(),
  ]);

  signedTx = await wallet.signTransaction({
    to: txData.to,
    data: txData.callData,                            // calldata field is `callData`, not `data`
    value: txData.value ? BigInt(txData.value) : 0n,
    from: wallet.address,
    chainId: txData.chainId,
    nonce: txData.nonce ?? nonce,
    gasLimit: txData.gas ? BigInt(txData.gas) : 1_500_000n,                 // Diamond proxy under-reports; floor at 1.5 M
    maxFeePerGas: txData.maxFeePerGas
      ? BigInt(txData.maxFeePerGas)
      : (feeData.maxFeePerGas ?? 0n) * 3n,                                  // headroom across the roundtrip
    maxPriorityFeePerGas: txData.maxPriorityFeePerGas
      ? BigInt(txData.maxPriorityFeePerGas)
      : (feeData.maxPriorityFeePerGas ?? 0n),
    type: 2,
  });
}
// Lighter offchain-api: nothing to sign here

// 3. Sign + submit execute-v2
const execTs = Date.now();
const execSig = await wallet.signMessage(
  `api/2/perp/execute-v2-${execTs}-${finalPayloadStr}`,
);

const execRes = await fetch('https://api.mobula.io/api/2/perp/execute-v2', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    action: data.action,
    dex: data.dex,
    chainId: data.chainId,
    marketId: data.marketId,
    transport: data.transport,
    payloadStr: finalPayloadStr,
    timestamp: execTs,
    signature: execSig,
    ...(signedTx && { signedTx }),
  }),
}).then(r => r.json());