Give every user of your product a wallet. Keep them yours.

const solace = (path, body) => fetch(BASE + path, {
  method: 'POST', body: JSON.stringify(body), headers: {
    Authorization: `Bearer ${KEY}`, 'Content-Type': 'application/json',
    'Idempotency-Key': crypto.randomUUID(),
  },
}).then((res) => res.json());

const user = await solace('/end-users', { external_id: 'cust_1042' });
const wallet = await solace(`/end-users/${user.id}/wallets`, {
  asset: 'USDC', network: 'ethereum',
});
// deposit.pending as it lands, deposit.confirmed once it's final —
// signed, and retried for about two days
await solace('/withdrawals', {
  end_user: user.id, asset: 'USDC', network: 'ethereum',
  address: '0x3fA9…8c21', amount: '250.00',
});

# 1 · An end user, under your own id for them
curl -X POST $BASE/end-users -u $KEY: \
  -H "Content-Type: application/json" \
  -d '{"external_id": "cust_1042"}'

# 2 · A wallet: a deposit address for a coin on a network
curl -X POST $BASE/end-users/eu_4kPq9Zm2xV7b/wallets -u $KEY: \
  -H "Content-Type: application/json" \
  -d '{"asset": "USDC", "network": "ethereum"}'

# 3 · A withdrawal, safe to retry with the same key
curl -X POST $BASE/withdrawals -u $KEY: \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"end_user": "eu_4kPq9Zm2xV7b", "asset": "USDC",
       "network": "ethereum", "address": "0x3fA9…8c21",
       "amount": "250.00"}'