> ## Documentation Index
> Fetch the complete documentation index at: https://next-developers.opencard.io/llms.txt
> Use this file to discover all available pages before exploring further.

# OpenCard Developers

> OpenCard developer hub — real-time card transactions, digital receipts, VAT, and webhooks for Expense Management Systems, card issuers, and receipt providers.

<div className="max-w-5xl mx-auto px-6 pt-12 pb-8">
  <div className="oc-glass-hero text-center">
    <h1 className="oc-hero-title">
      Build on OpenCard
    </h1>

    <p className="oc-hero-subtitle">
      Real-time card transactions, digital receipts, VAT, and line items — delivered to your systems via webhooks.
    </p>

    <div className="mt-8 flex flex-wrap gap-3 justify-center">
      <a href="https://sandbox-api.opencard.io/register" className="oc-btn-primary">
        Get API access
      </a>

      <a href="/getting-started/quickstart" className="oc-btn-secondary">
        Expense Management System quickstart →
      </a>
    </div>
  </div>
</div>

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  <CardGroup cols={2}>
    <Card title="Expense Management System" icon="building" href="/getting-started/quickstart">
      Orgs, card holders, webhooks. Receive `card.transaction.*` events in real time.
    </Card>

    <Card title="Expense Management System API" icon="code" href="/api-reference/ems/overview">
      Full API on `api.opencard.io` — TPAs, organizations, card holders, webhooks.
    </Card>

    <Card title="Card Issuers" icon="credit-card" href="/card-issuers">
      Deliver transactions to EMS apps, or fetch digital receipts via `receipts.opencard.io`.
    </Card>

    <Card title="Receipt Providers" icon="store" href="/receipt-providers">
      Collect merchant receipts and deliver them to OpenCard for Expense Management System enrichment.
    </Card>
  </CardGroup>
</div>

<div className="max-w-5xl mx-auto px-6 pb-16">
  <p className="oc-section-label mb-4">
    Explore further
  </p>

  <CardGroup cols={3}>
    <Card title="How it works" icon="sitemap" href="/introduction/how-it-works">
      Data model, event flow, and what OpenCard handles.
    </Card>

    <Card title="Authentication" icon="key" href="/getting-started/authentication">
      OAuth2 account\_client credentials and scopes.
    </Card>

    <Card title="Environments" icon="globe" href="/introduction/environments">
      Sandbox vs production URLs.
    </Card>

    <Card title="Webhooks" icon="webhook" href="/ems/webhooks/setup">
      Transactions, receipts, VAT, lifecycle events.
    </Card>

    <Card title="Digital Receipts API" icon="receipt" href="/api-reference/receipts/overview">
      `receipts.opencard.io` — publishers and callback requests.
    </Card>

    <Card title="Glossary" icon="book-open" href="/introduction/glossary">
      TPA, PDPC, card holder — every term explained.
    </Card>
  </CardGroup>
</div>