Which coins can I pay with?

You choose the coin and network on the payment page of our processor, NOWPayments, which lists the ones available for the invoice. Send only on the network that page names.

What if I send too little?

We credit the share that arrived, at the processor's quote, and the top-up shows as underpaid. You can then start another top-up for the rest.

Can I get a refund of a top-up?

No. Top-ups are final. You pay only for solved tasks, so start with a small top-up, from $10, and add more as you need it.

Billing

Pay for a Captcha API With Crypto: Top-ups, Receipts, Limits

How crypto top-ups work on ZeroCaptcha: invoices in US dollars, the hosted checkout, confirmations, under- and overpayments, receipts, and final top-ups.

3 min readPublished 30 September 2026Updated 1 October 2026

ZeroCaptcha is prepaid, and you add funds in crypto. There is no card, no subscription and no monthly invoice: you top up a US dollar balance, and each solved task is paid from it. This guide walks through a top-up from start to receipt, explains what happens when a payment is not exact, and covers the rules that protect your balance.

Why prepaid, and why crypto

A prepaid balance means you always know your maximum spend: tasks stop when the balance runs out, and nothing is billed after the fact. Crypto lets anyone pay without a card, from anywhere, and the payment processor, NOWPayments, handles the coins, networks and confirmations.

A top-up, step by step

Choose an amount. On Billing in the dashboard, pick or type an amount: $10 or more, with no maximum, in whole dollars or dollars and cents.
Continue to the payment page. The top-up becomes an invoice in US dollars on NOWPayments’ hosted checkout. There you choose the coin and see the exact amount, the address and the network to use. You pay the network’s fee.
Send the payment. Send exactly the amount shown, to the address shown, on the network named. Sending on another network, or another coin, may lose the funds.
Wait for confirmation. Back on Billing, the top-up shows as pending until the payment is confirmed on its network, then as paid. The balance is credited at once, and we email you.
Keep the receipt. Every credit gets a receipt, numbered without gaps, with the amount, the coin and network, and the time.

The Adding funds page in the docs has the full detail.

When the payment is not exact

Crypto payments are rarely perfect: wallets round, fees get deducted, people send twice. We credit what the processor reports as settled:

The top-up shows	What happened	What is credited
Paid	The invoice was paid	Its full amount
Underpaid	Less than the invoice arrived	The share that arrived, at the processor’s quote
Overpaid	More than the invoice arrived	All of it, at the processor’s quote
Expired	Nothing arrived before the invoice expired	Nothing; a payment that still arrives is credited

Coins sent on the wrong network, or of another coin, are not credited automatically. Write to us through the contact page with the transaction hash.

Top-ups are final

Top-ups are not refunded, in whole or in part: see the refund policy. What protects you instead:

You pay only for solved tasks. A task’s price is held while it runs; a task that fails or expires costs nothing, and its hold goes back at once. A task refused when you create it holds nothing.
You can start small. $10 is enough to try the API on real pages.
Keys can have a daily spend cap, so a bug cannot drain the balance in one day. See Secure your captcha API keys.
The low-balance email tells you once when your available balance falls below an amount you choose.

Checking your balance from code

Read the available balance before a large batch, so you never start work the balance cannot cover:

curl -s "$ZEROCAPTCHA_API/getBalance" \
  -H "Content-Type: application/json" \
  -d '{"clientKey": "'"$ZEROCAPTCHA_KEY"'"}'

{ "errorId": 0, "balance": 12.3456 }

The REST API has GET /v1/balance, and the 2Captcha format res.php?action=getbalance. A task your balance cannot cover is refused before it starts with ERROR_ZERO_BALANCE, at no charge. “Available” means what is left after prices held for tasks still running.

Company details on receipts

If you need a company name, postal address or tax ID on your receipts, add them under billing details in the dashboard. Nobody needs them to pay.

How much to add

Estimate your month from the number of forms you submit and the price per 1,000 on the pricing page; its estimator shows the top-up that covers a month. Captcha solving cost explains what moves the real cost. Then send your first task from the Cloudflare Turnstile solver page.