/ cat/snapshots/yourrepo

 {
 "error" : {
   "root_cause" : [
     {
       "type" : "repository_exception",
       "reason" : "[your_repo] Could not determine repository generation from root blobs"
     }
   ],
   "type" : "repository_exception",
   "reason" : "[your_repo] Could not determine repository generation from root blobs",
   "caused_by" : {
     "type" : "i_o_exception",
     "reason" : "Exception when listing blobs by prefix [index-]",
     "caused_by" : {
       "type" : "amazon_s3_exception",
       "reason" : "amazon_s3_exception: Access Denied (Service: Amazon S3; Status Code: 403; Error Code: AccessDenied; Request ID: 2P32JxxxxNQ1RT8T; S3 Extended Request ID: G/SURTMm9xuOXXXXIxnYXjC6JHo=)"
     }
   }
 },
 "status" : 500
}