Get your API key and use the API

Use this guide if you or a developer want to connect another system to Invoice Falcon, for example to fetch invoice PDFs into an ERP or accounting tool. By the end, you’ll have an API key and know where the full API reference lives.

Before you begin

• API access needs the Pro plan. Stores that installed before 8 July 2026 also have it on the Free plan.
• If you move to the Free plan, your API key is deleted and every integration using it stops working. After upgrading again, generate a new key and update your integrations.
• The key gives full access to your store’s invoices in Invoice Falcon. Share it only with people and systems you trust.

What the API can do

With the key, a system can work with your invoices (list, search, create, get the PDF, email to the customer, regenerate, and download several PDFs at once), your templates, your customers, and your Invoice Falcon settings. The full reference, with every request and example, is at docs.invoicefalcon.com.

Set it up

1. Open your Shopify admin and click Invoice Falcon in the left menu.
2. Click Settings in the app’s menu.
3. Click the Integrations tab.
4. In the API access section, under Access key, click Generate API key. An API key generated message appears.
5. Next to the API key field, click Copy.
6. Paste the key into your integration, or send it to your developer securely.

Your developer sends the key in the X-Auth-Token header of each request, as the note under the field says. The reference at docs.invoicefalcon.com covers the rest.

Replace your key

If the key may have leaked, or someone who had it shouldn’t any more:

1. On the Integrations tab, in the API access section, click Reset next to the API key field.
2. In the Reset API key window, click Reset.
3. Click Copy and update every integration with the new key.

The old key stops working immediately.

Check your setup

Ask your developer to make one simple request, such as listing invoices, with the new key. If it returns your invoices, the key works. If it returns an error, see Troubleshooting below.

Troubleshooting

Generate API key is greyed out

API access needs the Pro plan. Click Upgrade to Pro next to the button. See Invoice Falcon pricing and plans.

Requests fail with Invalid API key

The key was reset, deleted after a move to the Free plan, or copied wrongly. Open Settings > Integrations, copy the current key, and update your integration. If there’s no key, generate a new one.

Requests fail with API key is required

The request doesn’t include the key. Your developer needs to send it in the X-Auth-Token header.

Requests fail with REST API access requires a paid plan

Your store isn’t on the Pro plan. Upgrade, then generate a new key. See Invoice Falcon pricing and plans.

Requests fail with Rate limit exceeded

Your integration sent too many requests in a short time. Have it wait and retry. The limits are in the reference at docs.invoicefalcon.com.

FAQ

Does generating a key change anything in my store?

No. A key only allows requests. Nothing changes until an integration uses it.

Can I have more than one key?

No. Each store has one key. Use the same key for every integration, and update all of them when you reset it.

What happens to my integrations if I downgrade?

They stop working. Moving to the Free plan deletes the key. After upgrading again, generate a new key and update each integration. See Cancel or downgrade your plan.

Will customers notice anything?

Only if your integration emails them. Sending an invoice through the API sends the same invoice email as sending it from the order page.

Related guides

• Invoice Falcon pricing and plans, for what’s on Pro.
• Cancel or downgrade your plan, and what happens to your key.
• Email an invoice to a customer, for the email the API sends.