1. Get an API key
Sign in to app.arcuserp.com, open Settings, then click Developers. On the API Keys tab, click Create API key.- Name: give it a descriptive label (e.g.
My Integration) - Mode: choose Test for sandbox or Live for production
- Scopes: select at minimum
accounts:readto follow this guide
API keys are entity-scoped. The entity is encoded in the key itself, so the everyday resource routes are flat (for example
/v1/accounts and /v1/orders) and every request is automatically scoped to the entity that issued the key. You do not put the entity ID in the URL for these routes.When you need your entity ID
A small set of platform endpoints, such as the reconciliation and migration routes, use the/v1/entities/{entity_id}/... form. For those you need your entity ID, a UUID that identifies your organization in Arcus.
Easiest way: Go to Settings > Developers > API Keys. The Quick Reference panel at the top of the page shows your Entity ID with a copy button right next to it.
If you plan to call those platform endpoints, set the entity ID as an environment variable too:
2. Make your first request
List the first five accounts in your entity:3. Understand the response
Every list endpoint returns the same envelope:starting_after with the id of the last record in data:
4. Create your first order
Next steps
Authentication
Entity-scoped keys, scopes, and IP allowlists.
Concepts
Idempotency, pagination, expand, errors, and more.
API Reference
Every endpoint documented with try-it-now.
Webhooks
Subscribe to real-time order, payment, and fulfillment events.

