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Sandbox Testing for eSIM APIs: Build Your Integration Before You Pay
An eSIM API sandbox lets you build and test orders, top-ups and refunds with test keys and a sample catalogue, without spending money or creating real eSIMs. Fully Signal's sandbox gives every partner a test key, a €1,000 test balance, sample destinations and prices, sample orders in every eSIM state, and scenarios for hard-to-reproduce outcomes.
In this article
The worst way to test an eSIM integration is with real money and real customers. A good sandbox lets your developers build everything first. Here's how to use one well, using the Fully Signal sandbox as the example.
What the Fully Signal sandbox includes
- Test keys (
fsk_test_…) you create in the partner panel — no deposit needed - A sample catalogue — made-up destinations ("Country 1", "Region 1"…) and prices in the same shapes as the live catalogue
- A €1,000 test balance that only test orders spend and test refunds give back
- Four sample orders, one per eSIM state, so read endpoints answer from day one
- Working install and QR links, so you can try your own emails and pages
- Scenarios for outcomes that are hard to cause on purpose: a pending order, an insufficient-balance (402) response, a refund held for review
- A reset button that empties the sandbox and starts fresh
Nothing touches a real network: sandbox eSIMs can't be installed on a phone, and test keys never see live data (or vice versa).
Why same-shape data matters
Because sample responses have exactly the shape of live ones, an integration built on a test key goes live by changing the key. No second round of development.
What to test
| Flow | Test |
|---|---|
| Catalogue | List destinations and packages; store package IDs |
| Order | Create an order; read it back by ID and by your own reference |
| Idempotency | Repeat a request with the same Idempotency-Key — no second order |
| Pending | Use the pending scenario; make sure your UI waits correctly |
| Low balance | Use the 402 scenario; alert your team, don't crash checkout |
| Top-up | Top up a sample eSIM; read its top-up history |
| Refund | Refund an order; handle the "held for review" scenario |
| Delivery | Open the install link and QR from your own email template |
Go-live checklist
- All flows above pass on the test key
- Live key stored on your server only, never in a browser or app
- Live key restricted with the narrowest scopes and an IP allowlist
- Webhook URL set and signature verification tested
- First deposit made — this unlocks the live catalogue, your wholesale prices and live keys
- Auto top-up or low-balance alerts turned on
- Package IDs re-synced from the live catalogue (sample IDs differ)
FAQ
Is the eSIM API sandbox free?
Yes. Every Fully Signal account can use the sandbox with test keys, a test balance and sample data at no cost.
Can I install a sandbox eSIM on my phone?
No. Sandbox eSIMs point to a test address, so scanning one installs nothing. The install page and QR link still work so you can test your delivery emails.
Do sample package IDs work with live keys?
No. The sample catalogue uses made-up destinations. After your first deposit, sync the live catalogue and use its package IDs.
Can I reset the sandbox?
Yes, from the panel's API key settings. The next API call starts a fresh sandbox.
