StellarRefund.js

// load escrow account from pub key
const escrowAccount = await blockchain.loadAccount(escrowPubKey)

// build claim transaction with timelock
const tb = new stellarSdk.TransactionBuilder(escrowAccount, {
  timebounds: {
    minTime: Math.floor(Date.now() / 1000) + 3600, // this envelope is valid after 1 hour
    maxTime: 0
  }
})
.addOperation(
  stellarSdk.Operation.payment({
    destination: serverKeyPair.publicKey(),
    asset: stellarSdk.Asset.native(),
    amount: '2.00001' // send upfront cost back to server 
  }))
.addOperation(
  stellarSdk.Operation.accountMerge({
    destination: userPubKey // merge remainder back to user
  }))
.build()

// sign transaction
tx.sign(serverKeyPair)

// https://www.stellar.org/developers/js-stellar-sdk/reference/examples.html
const refundEnvelope = tx.toEnvelope().toXDR('base64')