Get paid in crypto.
Settle on your terms.

BODY='{"amount":"49.00","currency":"USD","order_id":"1024"}'
TS=$(date +%s)
SIG=$(printf '%s\nPOST\n/api/v1/invoices\n%s' "$TS" "$BODY" \
  | openssl dgst -sha256 -hmac "$CRYPTAIN_SECRET" | cut -d' ' -f2)

curl https://cryptain.net/api/v1/invoices \
  -H "Content-Type: application/json" \
  -H "X-Api-Key: $CRYPTAIN_KEY" -H "X-Timestamp: $TS" \
  -H "X-Signature-Version: 2" -H "X-Signature: $SIG" \
  -d "$BODY"

$body = json_encode(['amount' => '49.00', 'currency' => 'USD', 'order_id' => '1024']);
$ts   = (string) time();
$sig  = hash_hmac('sha256', "$ts\nPOST\n/api/v1/invoices\n$body", $secret);

$ch = curl_init('https://cryptain.net/api/v1/invoices');
curl_setopt_array($ch, [
    CURLOPT_POST => true, CURLOPT_POSTFIELDS => $body, CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => ['Content-Type: application/json', "X-Api-Key: $key",
        "X-Timestamp: $ts", 'X-Signature-Version: 2', "X-Signature: $sig"],
]);
$invoice = json_decode(curl_exec($ch), true)['data'];
header('Location: ' . $invoice['checkout_url']);

import crypto from 'node:crypto';

const body = JSON.stringify({ amount: '49.00', currency: 'USD', order_id: '1024' });
const ts = Math.floor(Date.now() / 1000).toString();
const sig = crypto.createHmac('sha256', process.env.CRYPTAIN_SECRET)
  .update([ts, 'POST', '/api/v1/invoices', body].join('\n')).digest('hex');

const res = await fetch('https://cryptain.net/api/v1/invoices', { method: 'POST', body, headers: {
  'Content-Type': 'application/json', 'X-Api-Key': process.env.CRYPTAIN_KEY,
  'X-Timestamp': ts, 'X-Signature-Version': '2', 'X-Signature': sig } });
const { data: invoice } = await res.json();

import hashlib, hmac, json, os, time, requests

body = json.dumps({"amount": "49.00", "currency": "USD", "order_id": "1024"})
ts = str(int(time.time()))
msg = "\n".join([ts, "POST", "/api/v1/invoices", body]).encode()
sig = hmac.new(os.environ["CRYPTAIN_SECRET"].encode(), msg, hashlib.sha256).hexdigest()

invoice = requests.post("https://cryptain.net/api/v1/invoices", data=body, headers={
    "Content-Type": "application/json", "X-Api-Key": os.environ["CRYPTAIN_KEY"],
    "X-Timestamp": ts, "X-Signature-Version": "2", "X-Signature": sig,
}).json()["data"]

{
  "event": "invoice.paid",
  "data": {
    "order_id": "1024", "status": "paid",
    "amount": "49.00", "currency": "USD",
    "pay_currency": "USDT_TRC20", "paid_amount": "49.00"
  }
}