Flutter jsonwebtoken generate Appstore Connect API token invalid - flutter

Question

I am trying to generate a Appstore Connect API token to manage my apps. The package I am using is dart_jsonwebtoken. The code:
final jwt = JWT({
"iss": "YOUR_ISSUER_ID",
"iat": DateTime.now().millisecondsSinceEpoch / 1000,
"exp": DateTime.now().add(Duration(days: 30)).millisecondsSinceEpoch / 1000,
"aud": "appstoreconnect-v1",
"scope": [
"GET /v1/apps?filter[platform]=IOS"
]
}, header: {
"alg": "ES256",
"kid": "YOUR PRIVATE KEY ID",
"typ": "JWT"
});
// Here I use the content from AuthKey_KEYID.p8 file
final token = jwt.sign(ECPrivateKey('''-----BEGIN PRIVATE KEY-----
YOUR AuthKey Content
-----END PRIVATE KEY-----'''), algorithm: JWTAlgorithm.ES256);
print('Signed token: $token\n');
The token is generated successfully, and I am using it to call the API, but I am getting an invalid token error:
{
"errors": [
{
"status": "401",
"code": "NOT_AUTHORIZED",
"title": "Authentication credentials are missing or invalid.",
"detail": "Provide a properly configured and signed bearer token, and make sure that it has not expired. Learn more about Generating Tokens for API Requests https://developer.apple.com/go/?id=api-generating-tokens"
}
]
}
I am pretty sure there is some wrong with my code to generate the token. Can somebody help me with that? Thanks in advance.
I got it working by using below ruby code. The generated token is working fine. I am trying to rewrite it using flutter.
require "base64"
require "jwt"
ISSUER_ID = "2ece1127-df4d-426a-a3eb-061e68f5eebe"
KEY_ID = "W9M2AM584Y"
private_key = OpenSSL::PKey.read(File.read('AuthKey_W9M2AM584Y.p8'))
token = JWT.encode(
{
iss: ISSUER_ID,
exp: Time.now.to_i + 20 * 60,
aud: "appstoreconnect-v1"
},
private_key,
"ES256",
header_fields={
kid: KEY_ID }
)
puts token