4 APIs to Automate Expense Reporting: Receipt Scan Slack Approval Payout

#tooling #api

Every finance manager has a folder they don't talk about.

A quiet accumulation of receipt photos, Slack forwards, and email attachments with subjects like "pls reimburse ty." It grows a little every week, an it never shrinks on its own.

Here's how to stop feeding that folder, with a scan to bank transfer automated workflow.

The workflow

Employee submits a receipt → Veryfi extracts the data → Slack sends the manager an approve/reject message → QuickBooks logs the expense → Wise transfers the reimbursement.

API #1 — Veryfi (receipt OCR)

Veryfi takes a receipt image or PDF and returns structured JSON in seconds: vendor name, date, total amount, line items, currency, and tax.

It's pre-trained on hundreds of millions of receipts and works across 38 languages and 91 currencies.

No model training required on your end.

POST https://api.veryfi.com/api/v8/partner/documents/

Headers:
  CLIENT-ID: your_client_id
  AUTHORIZATION: apikey your_username:your_api_key
  Content-Type: application/json

{
  "file_url": "https://your-storage.com/receipts/receipt-001.jpg",
  "tags": ["expense", "reimbursement"],
  "categories": ["Meals", "Travel", "Office Supplies"]
}

The response gives you total, vendor.name, date, currency_code, and a full line_items array. All of that feeds into the Slack message in the next step.

API #2 — Slack (manager approval)

Rather than routing approvals through email, you send the manager an interactive Slack message using Block Kit - Slack's UI framework for composing messages with buttons and structured data.

The manager sees the receipt details and clicks Approve or Reject directly in Slack.

POST https://slack.com/api/chat.postMessage

Headers:
  Authorization: Bearer xoxb-your-bot-token
  Content-Type: application/json

{
  "channel": "manager-slack-user-id",
  "text": "New expense reimbursement request",
  "blocks": [
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "*New expense request*\n*Employee:* John Doe\n*Vendor:* Marriott\n*Amount:* USD 189.00\n*Date:* 2025-03-10"
      }
    },
    {
      "type": "actions",
      "elements": [
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "Approve" },
          "style": "primary",
          "action_id": "approve_expense",
          "value": "expense_id_123"
        },
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "Reject" },
          "style": "danger",
          "action_id": "reject_expense",
          "value": "expense_id_123"
        }
      ]
    }
  ]
}

When the manager clicks a button, Slack sends an interaction payload to your app's endpoint with the action_id and value. You use that to trigger the next step.

Tips: You'll need to enable Interactivity in your Slack app settings and provide a Request URL — that's the endpoint your app exposes to receive button click payloads. Test this locally first using a tunnel like ngrok before deploying.

API #3 — QuickBooks (accounting sync)

Once approved, you log the expense in QuickBooks Online via the Purchase endpoint. This creates a record in the books against the right account and employee.

POST https://quickbooks.api.intuit.com/v3/company/{realmId}/purchase

Headers:
  Authorization: Bearer your_oauth2_access_token
  Content-Type: application/json
  Accept: application/json

{
  "PaymentType": "Cash",
  "AccountRef": { "value": "35", "name": "Checking" },
  "EntityRef": { "value": "employee_id", "type": "Employee" },
  "TotalAmt": 189.00,
  "Line": [
    {
      "Amount": 189.00,
      "DetailType": "AccountBasedExpenseLineDetail",
      "AccountBasedExpenseLineDetail": {
        "AccountRef": { "value": "7", "name": "Travel" }
      }
    }
  ]
}

API #4 — Wise (reimbursement payout)

Wise handles the actual bank transfer to the employee.

It's API-first, uses the mid-market exchange rate with a flat transparent fee, and works for both domestic and international payouts across 40+ currencies.

The payout flow is three calls: create a quote, create the transfer, then fund it.

# Step 1 — Create a quote
POST https://api.wise.com/v3/profiles/{profileId}/quotes

{
  "sourceCurrency": "USD",
  "targetCurrency": "USD",
  "sourceAmount": 189.00,
  "targetAccount": "<recipient_account_id>"
}

# Step 2 — Create the transfer
POST https://api.wise.com/v1/transfers

{
  "targetAccount": "<recipient_account_id>",
  "quoteUuid": "<quote_id_from_step_1>",
  "customerTransactionId": "expense_id_123",
  "details": { "reference": "Expense reimbursement — March 2025" }
}

# Step 3 — Fund the transfer
POST https://api.wise.com/v3/profiles/{profileId}/transfers/{transferId}/payments

{
  "type": "BALANCE"
}