curl --request POST \
  --url https://api.privy.io/v1/wallets/{wallet_id}/rpc \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --header 'privy-app-id: <privy-app-id>' \
  --data '{
  "method": "secp256k1_sign",
  "params": {
    "hash": "0x12345678",
  }
}'

{
  "method": "secp256k1_sign",
  "data": {
    "signature": "0x0db9c7bd881045cbba28c347de6cc32a653e15d7f6f2f1cec21d645f402a64196e877eb45d3041f8d2ab1a76f57f408b63894cfc6f339d8f584bd26efceae3081c",
    "encoding": "hex"
  }
}