Company A, with an AWS account named Account A, has recently acquired Company B, which has an AWS account named Account B. Company B stores its data in an Amazon S3 bucket. To facilitate the acquisition, administrators need to grant a user from Account A full access to the S3 bucket in Account B. Despite configuring the necessary IAM permissions for the user in Account A, the user is unable to access the files in the S3 bucket. What solution should be implemented to resolve this access issue?