AwsS3Client exception : Access Denied to S3 while exporting data


I am trying to export data to an external S3 bucket from C3 tenant. Even though the bucket policy associated with the bucket has Full Access to the C3 IAM role. I am unable to export data or write a file on the bucket. Moreover, I am getting the same error, when trying to write a simple S3File object on the bucket. However, I could list files in the bucket.

I could check the permissions on the bucket by :AwsS3Bucket.fromName(’’).getResource().grants.

1.Is it the right way to check for permissions?
2.What should I do to elevate the permissions on an external bucket from a platform standpoint?.