Unity AWS S3 GetPreSignedURLAsync is not working on android

Hi, Using Unity AWS libraries, AmazonS3Client.GetPreSignedURLAsync () is working well on windows but not on android. The callback is never called. Any ideas what is going on?

First the auth is using cognito:

 _credentials = new CognitoAWSCredentials(IdentityPoolId, _CognitoPoolRegion);
 _s3Client = new AmazonS3Client(_credentials, _S3ClientRegion);

The code using it :

GetPreSignedUrlRequest request = new GetPreSignedUrlRequest
{
    BucketName = bucketName,
    Key = url,
    Expires = DateTime.Now.AddHours(S3_ASSET_EXPIRATION_HOURS)
};
Debug.Log("AWS asking to sign: " + url);
Debug.Log("AWS " + Credentials != null ? Credentials.ToString() : "Null");
Debug.Log("AWS " + Credentials.IdentityPoolId);

S3Client.GetPreSignedURLAsync(request, (response)  => {

    // *** This is never called on Android

    Debug.Log("AWS Signed response: " + response.Response.HttpStatusCode);
    
    if (response.Exception == null)
    {
        Debug.Log("AWS: Found signed URL " + response.Response.Url);
        tcs.SetResult(response.Response.Url);
    }
    else
    {
        tcs.SetResult("");
        Debug.LogError("[GetUrl] GetPresignedURL failed with exception: " + response.Exception.ToString());
    }
});

Thanks !