Six calls to run a transaction.

// What tax is due, at this address, on this category.
const res = await fetch("https://maxafi.com/taxafi/v1/calculate", {
  method:  "POST",
  headers: {
    "X-Api-Key":         "tx_...",
    "X-Idempotency-Key": "txn_88231",
    "Content-Type":     "application/json"
  },
  body: JSON.stringify({
    amount:        100.00,     // decimal dollars
    category_code: "GEN",
    ship_to: {                // the CONSUMER address, not the merchant
      street: "1100 Congress Ave",
      city:   "Austin",
      state:  "TX",
      zip:    "78701"
    }
  })
});

// response
{
  "combined_rate": 0.0825,
  "tax_total": 8.25, "total": 108.25,
  "resolution": { "confidence": "zip", "resolver": "zip5" },
  "breakdown": [
    { "name": "Texas",  "level": "state", "rate": 0.0625, "tax": 6.25 },
    { "name": "Austin", "level": "city",  "rate": 0.02,   "tax": 2.00 }
  ],
  "data_verified": true
}

// Take a payment. Six calls, this is the middle one.
const res = await fetch("https://api.dapit.com/v1/payments", {
  method:  "POST",
  headers: {
    "X-Api-Key":         key,
    "X-Idempotency-Key": crypto.randomUUID(),
    "Content-Type":     "application/json"
  },
  body: JSON.stringify({
    amount:    4250,          // minor units
    currency:  "USD",
    capture:   true,
    reference: "job-10482"
  })
});

const { success, payment, meta } = await res.json();
// meta.request_id is what support will ask you for