Free trial abuse: one trial per person, not per email

The threat

A trial costs compute, support and sometimes real money such as SMS or API usage. Serial trial users never convert, and they distort your funnel numbers.

What we stop

• A second trial from the same device, even with a new email address.
• A second trial in another browser on the same computer.
• Several trials from one household or network, including from a phone on the home Wi-Fi.
• Trials claimed through disposable email addresses and plus-tag variants.
• Scripted trial sign-ups.

Refunds and fairness

If a trial was granted by mistake or is refunded, release the claim and the device can claim again, within a bound that stops a claim and refund loop. A deny always carries a reason, so a genuine customer can be sent to a paid plan instead of a dead end.

Gate the trial

// Backend, after the app sends the attestation unchanged
const d = await (await fetch('https://api.fpchecker.com/v1/eligibility', {
  method: 'POST',
  headers: { 'content-type': 'application/json', 'X-Secret-Key': process.env.FPCHECKER_SECRET_KEY },
  body: JSON.stringify({ attestation, email, claim: true, kind: 'trial', subject: session.userId, clientIp }),
})).json();
// Start the trial only when d.eligible is true; send d.reason to your logs.
return { eligible: d.eligible === true, action: d.action, reason: d.reason, powDifficulty: d.powDifficulty };

Frequently asked questions