generateSignature function
Implementation
String generateSignature(String message, String apiKey) {
List<int> secretBytes = utf8.encode(apiKey); // Corrected encoding
List<int> messageBytes = utf8.encode(message);
var hmac = Hmac(sha256, secretBytes); // Create HMAC instance
var digest = hmac.convert(messageBytes); // Compute hash
var hash = base64Encode(digest.bytes); // Encode to Base64
return hash;
}