Approva REST API and webhooks: reference

Approva REST API & Webhooks (v1.1)

Approva ships a JSON REST API and signed webhooks so purchase approvals can plug into Power Automate, Zapier, n8n, or your own code — including Microsoft Business Central integrations built against it.

Authentication

Create a key in Settings → API & Webhooks (admin). A key belongs to a user and can do exactly what that user can do in the app — requester keys raise requests, approver keys approve (never their own requests), admin keys can issue POs. Send it on every call:

Authorization: Bearer apk_...

The key is shown once at creation and stored hashed. Revoke any time.

Endpoints

Method & path	What it does
`GET /api/ping`	Verify a key; returns the acting user + role
`GET /api/requests`	Newest 50 requests; `?status=` filters (`draft`, `pending`, `partially_approved`, `approved`, `rejected`, `po_issued`)
`POST /api/requests`	Create a request (optionally `"submit": true`)
`GET /api/requests/{id}`	One request with lines, approvals, PO
`POST /api/requests/{id}/submit`	Submit a draft for approval
`POST /api/requests/{id}/approve`	Approve at the next level (body: `{"note": "..."}` optional)
`POST /api/requests/{id}/reject`	Reject (halts the request)
`POST /api/requests/{id}/generate-po`	Issue the numbered PO (admin; fully approved only)
`GET /api/pos`	List purchase orders
`GET /api/vendors` · `GET /api/cost-centers`	Reference data
`GET /api/openapi.json`	OpenAPI 3 spec (no auth) — machine-readable version of this table

Create a request

curl -X POST https://your-install/api/requests \
  -H "Authorization: Bearer apk_..." -H "Content-Type: application/json" \
  -d '{
    "vendor": "Northwind Supplies",
    "cost_center": "OPS",
    "justification": "Replacement toner for the print room",
    "submit": true,
    "lines": [
      {"description": "Toner cartridge X-42", "qty": "4", "unit": "89.50"}
    ]
  }'

Money is decimal-in, integer-cents-out: send "unit": "89.50", read "unit_cents": 8950. All the same validation and approval-threshold math as the UI applies.

Webhooks

Add receiver URLs in Settings → API & Webhooks. Events:

request.submitted — a request entered the approval flow
request.approved — a request became FULLY approved (not each level)
request.rejected — an approver rejected it
po.issued — a purchase order was generated

Each delivery is an HTTP POST with a JSON body ({"event", "at", "request": {...}}) and:

X-Approva-Event: request.approved
X-Approva-Signature: sha256=<hex HMAC-SHA256 of the raw body, keyed with the endpoint's secret>

Verify the signature before trusting a payload. Delivery is one attempt with a 5-second timeout — deliberately simple; the Recent deliveries log on the settings page shows every attempt and response code. Design receivers to be idempotent.

Power Automate (and Logic Apps)

Two ways, no Microsoft partnership required:

Instant trigger via webhook: in Power Automate, create a flow with the "When an HTTP request is received" trigger, copy its URL into Approva's webhooks, and branch on body('...')?['event']. That's approvals driving Teams messages, Business Central jobs, or anything else in your tenant.
Custom connector: Power Automate → Data → Custom connectors → **Import an OpenAPI file** → point it at /api/openapi.json from your install (or download the file). Set security to API Key / Bearer. Every endpoint above becomes a native action.

Limits, honestly

The API acts at user level; there is no separate scope system beyond the app's roles.
One delivery attempt per webhook event (log + idempotent receivers, not a retry queue).
List endpoints cap at 50–100 rows; this is an SMB approval tool, not a data warehouse.

MCP — the agent door (new in 3.0)

Approva speaks the Model Context Protocol at POST /mcp, so Claude, ChatGPT agents, n8n's AI nodes or your own code can use Approva instead of merely reading it. It is the same product underneath: the same bearer key, the same roles, and the same approval guards. An agent cannot do anything its key's user could not do in the browser.

Transport is streamable HTTP, stateless: one JSON-RPC 2.0 request in, one JSON response out. No session to keep, nothing to clean up — the right shape for a self-hosted app.

curl -s -X POST https://approva.example.com/mcp \
  -H "Authorization: Bearer apk_xxxx" -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize",
       "params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"my-agent","version":"1"}}}'

Then tools/list to discover, tools/call to act:

curl -s -X POST https://approva.example.com/mcp \
  -H "Authorization: Bearer apk_xxxx" -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/call",
       "params":{"name":"pending_report","arguments":{}}}'

Connect it to an assistant

Mint the key in the app first: Settings → API keys. Choose Read only when the assistant should answer questions but never change anything — the endpoint then lists only the read tools and refuses the rest by name, so a careless prompt cannot write. Full access behaves as before.

Every client needs the same three facts, and nothing in the handshake is vendor-specific:


The address	`https://approva.example.com/mcp`
The key	header `Authorization: Bearer apk_xxxx`
The transport	MCP over streamable HTTP, stateless

Claude — one command, or the same URL and header as a custom connector in the desktop and web apps:

claude mcp add --transport http approva https://approva.example.com/mcp \
  --header "Authorization: Bearer apk_xxxx"

ChatGPT and the OpenAI API — one entry in the Responses API's tools array (in ChatGPT itself, the same URL and key go in as a connector):

{
  "type": "mcp",
  "server_label": "approva",
  "server_url": "https://approva.example.com/mcp",
  "authorization": "apk_xxxx",
  "require_approval": "never"
}

Own Your AI reads a list of servers in this shape:

{
  "mcpServers": [
    { "id": "approva", "name": "Approva", "url": "https://approva.example.com/mcp",
      "token": "apk_xxxx", "enabled": true }
  ]
}

**Every other client spells the same three facts differently — copy the shape from its own documentation, not from here.** VS Code is the clearest example of why: its configuration reference (read 6 September 2026) puts servers in .vscode/mcp.json under a "servers" object — *"an object that maps server names to their configurations"* — not an mcpServers array. Pasted as-is, the block above will not load there. The id, the URL and the token are what travel; the JSON around them belongs to whichever client you are configuring.

A local model, n8n, or your own code — n8n's MCP Client node takes the URL and the same Authorization: Bearer header; a model running on your own machine reaches it through any MCP client, so nothing leaves your network at all. Writing it yourself is one POST of JSON-RPC 2.0:

curl -X POST https://approva.example.com/mcp \
  -H "Authorization: Bearer apk_xxxx" -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Any client that speaks MCP's streamable-HTTP transport works, including ones that do not exist yet: Approva implements the protocol, not an integration with a particular vendor.

Tools

Tool	Writes?	What it does
`list_requests`	no	Requests newest first (max 50); optional `status` filter
`get_request`	no	One request with lines, approvals and PO
`create_request`	yes	Creates a request; `submit: true` sends it for approval
`submit_request`	yes	Submits a draft (requester or admin only)
`approve_request`	yes	Records an approval — full guard applies
`reject_request`	yes	Records a rejection (terminal)
`pending_report`	no	Counts by status + everything awaiting a decision
`list_vendors`	no	Vendors on file
`list_cost_centers`	no	Cost centers on file

There is deliberately no issue_po tool. Issuing a purchase order is the moment money becomes committed to a supplier; that stays a human click in the app, and the REST API keeps it behind the admin role. An agent can tell you a request is ready — it cannot cut the PO.

What the guard does to an agent

The rules are the product, so they apply identically here:

Approving your own request is refused: "You cannot approve your own request."
A second decision by the same person is refused: "You have already recorded a decision on this request."
A decision after the workflow closed is refused: "This request is no longer awaiting approval."
Under a delegation, the delegator's own requests are refused, and delegator + delegate can never both be counted on one request.

Refusals come back as a tool result with isError: true and the sentence above, so the model can read what happened and correct itself, rather than a bare protocol error.

Argument hygiene

Every argument must be a single value. Send a list or an object where text belongs and the call is refused by name — lines on create_request is the one allowlisted exception, because a request genuinely carries line items:

{"content":[{"type":"text","text":"vendor must be a single text or number value, not a list or object."}],"isError":true}

Unknown arguments are refused by name too (Unknown argument: vendorr), because an agent that typos a field should be told, not silently half-obeyed. Missing required arguments, wrong types and out-of-enum values are all named the same way.

Errors

Protocol problems are JSON-RPC errors: -32700 (bad JSON), -32600 (batch requests, which are not supported), -32601 (unknown method), -32602 (unknown tool). Domain refusals are tool results with isError: true. GET /mcp answers 405 with Allow: POST.