Adding additional policies to the IAM role still did not work for me. This video got me the basics https://www.bing.com/videos/riverview/relatedvideo?&q=step+by+step+to+configure+RDS+SQL+restore+from+S3&&mid=C387ABE5AC396000E939C387ABE5AC396000E939&&mcid=507E1C5F5F944F0BB9504BE3A01DA122&FORM=VRDGAR
But it was still failing until I reset the master rds password!