--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": "signMessageWithIdentityKey",
  "network": "MAINNET",
  "params": {
    "message": "Hello, Spark!",
    "compact": true
  }
}'

{
  "method": "signMessageWithIdentityKey",
  "data": {
    "signature": "304402201a2b3c4d5e6f708192a3b4c5d6e7f8091a2b3c4d5e6f708192a3b4c5d6e7f80902201a2b3c4d5e6f708192a3b4c5d6e7f8091a2b3c4d5e6f708192a3b4c5d6e7f809"
  }
}