I created user with full admin access and then i used that user creds to run terraform code to create backup vault/plan and create role to run it .
However , if i create backup using the new role created from terraform backup fails with above error. However , if i create backup of same server using role i created manually in GUI seems to work.
both roles have correct perms as following:
arn:aws:iam::aws:policy/service-role/AWSBackupServiceRolePolicyForBackup
arn:aws:iam::aws:policy/service-role/AWSBackupServiceRolePolicyForRestores