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": "signMessage",
  "params": {
    "message": "aGVsbG8sIFByaXZ5IQ=",
    "encoding": "base64"
  }
}
'

{
  "method": "signMessage",
  "data": {
    "signature": "76wpEsq9FS4QOInePQUY3b4GCXdVwLv+nNp4NnI+EPTAPVwvXCjzjUW/gD6Vuh4KaD+7p2X4MaTu6xYu0rMTAA==",
    "encoding": "base64"
  }
}