Invoices → accounting

This guide connects MendriX invoicing to your accounting system: pull finalized invoices out, and post payments back in. It uses the Invoice service (list/get/patch/finalize/cancel/delete, plus payments).

Beta API

The Invoice API is in beta: paths, fields and behaviour may still change without notice. Keep this in mind before building a production integration on it. The Core API reference marks every beta endpoint with a Beta badge.

Invoice lifecycle

Invoices start preliminary and become finalized. Several fields are patchable only while preliminary; once finalized they are locked (see Errors & conventions). Pull finalized invoices into accounting; keep editing on the preliminary ones.

Step 1 — Pull finalized invoices (incremental)

Manual (REST)

# Page finalized invoices changed since your last run.
curl "$MENDRIX_BASE/invoice/invoices/?since=$WATERMARK&limit=1000" \
  -H "Authorization: Bearer $MENDRIX_ACCESS_TOKEN" \
  -H "Accept: application/json"

const since = loadWatermark() || 1;     // sequence number; 1 on the first run
const params = new URLSearchParams({ limit: '1000', since });

const state = {};
for await (const invoice of listAll('/invoice/invoices/', params, state)) {
  if (isFinalized(invoice)) {
    postInvoiceToAccounting(invoice);   // your side
  }
}
saveWatermark(state.maxSequence);       // once, at the end of the cycle

Fetch a single invoice’s full detail with GET /invoice/invoices/{invoiceId} when you need line-level data.

n8n

1. Schedule Trigger — e.g. hourly.
2. HTTP Request Get access token — the login node from Using n8n (Custom Auth = MendriX API token).
3. HTTP Request (GET /invoice/invoices/): Authorization header = Bearer {{ $('Get access token').first().json.data.items[0].access }}, query limit=1000 and since={{ $json.watermark }}; enable pagination.
4. Filter node — keep only finalized invoices.
5. Map fields and create/update the invoice in your accounting system.
6. Store data.maxSequence from the last page as the next watermark — it is a sequence number, not a date (see Pagination & sync).

Importable workflow: invoices-accounting.json.

Step 2 — Post payments back

When your accounting system registers a payment, record it against the MendriX invoice:

Manual (REST)

curl -X POST "$MENDRIX_BASE/invoice/invoices/INVOICE_ID/payments" \
  -H "Authorization: Bearer $MENDRIX_ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{ "amount": 1250.00, "date": "2026-07-21", "reference": "BANK-TXN-8842" }'

List or remove payments:

curl "$MENDRIX_BASE/invoice/invoices/INVOICE_ID/payments" \
  -H "Authorization: Bearer $MENDRIX_ACCESS_TOKEN"

curl -X DELETE \
  "$MENDRIX_BASE/invoice/invoices/INVOICE_ID/payments/PAYMENT_ID" \
  -H "Authorization: Bearer $MENDRIX_ACCESS_TOKEN"

Refer to the reference for the exact payment body.

n8n

1. Trigger on a payment event from your accounting system (Webhook or Schedule).
2. HTTP Request Get access token — the login node from Using n8n.
3. HTTP Request (POST /invoice/invoices/{{ $json.invoiceId }}/payments), Authorization header = Bearer {{ $('Get access token').first().json.data.items[0].access }}, JSON body with amount, date, reference.
4. Handle errors (e.g. invoice not found / already paid) via the error output.

Other invoice operations

The Invoice service also supports, via REST (see the reference):

• POST /invoice/invoices/{invoiceId}/finalize — finalize a preliminary invoice.
• POST /invoice/invoices/{invoiceId}/cancel — cancel an invoice.
• DELETE /invoice/invoices/{invoiceId} — delete a preliminary invoice.
• PATCH /invoice/invoices/{invoiceId} — merge-patch (preliminary-only fields apply while preliminary).

Reconciliation tips

• Match on a stable key (MendriX invoice id ↔ your accounting reference).
• Idempotent payment posting — guard against posting the same bank transaction twice (dedupe on reference).
• Watermark after success so a failed run safely re-reads next time.