Use the Halyard API

The Halyard API lets your own app create customers, send invoices and read payments. It's available on the Growth and Scale plans; see Change your plan.

Create an API key#

1. Open Settings → Developers → API keys.
2. Click New key, name it after the app that will use it, and choose its permissions.
3. Copy the key. It's shown once.

Keys starting with hk_test_ work with test data; hk_live_ keys work with real data.

Make your first request#

curl https://api.halyard.app/v1/invoices \
  -H "Authorization: Bearer hk_test_4f2a…" \
  -d customer=cus_81Hd2 \
  -d "lines[0][description]=Consulting, March" \
  -d "lines[0][amount]=120000" \
  -d currency=eur

Amounts are in the smallest currency unit: 120000 is €1,200.00.

Limits#

Plan	Requests per minute
Growth	100
Scale	1,000

Over the limit, the API answers 429 Too Many Requests with a Retry-After header.

Tip: don't poll for payments. Set up webhooks and we'll tell your app the moment something changes.