@girish Thanks for looking into it and I tried again with the Amazon S3 backup option in my server, and it started working for me as well (after you said that you enabled it within your AWS Account.
I think that might have been the main issue as the error message called out that it couldn't object cloudron-testfile (which it might do through the Cloudron AWS Account if it exists*), so if the region wasn't enabled within that account, it wouldn't be able find the correct endpoint to use for that test file and hence wouldn't know where the correct endpoint is.
I say that with the typo that you identified in the backup config code and enabling the AWS Melbourne region within your AWS account, that managed to get it working. In any ways, thanks for looking into this and getting it working for me 🙂