I feel bad to give you this help article. Lots of steps: https://community.intuit.com/articles/1197814-error-h101-h202-h303-or-h505-when-opening-your-company-file

Resolution for 'backup procedure issue: 'Can’t open a backup copy of my company file that my accountant has sent back. It’s a simple restore backup procedure but I get the H505 error every time. Not on a server' available: Yes.

The backup procedure issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the backup procedure issue yourself by looking for a resolution described in the article. If it is a complex backup procedure issue or you are unable to solve the issue, you may contact us by clicking here or by using other backup procedure support options.

For more information about resolving issues related to backup procedure in Quickbooks/QBO or to get support for the issue 'Can’t open a backup copy of my company file that my accountant has sent back. It’s a simple restore backup procedure but I get the H505 error every time. Not on a server', click the link below: