If I enter the bill backdated, then I’ll end up with the same expense on QB twice – I have already put the bill down as an expense (and marked it as paid by credit card) so to enter it again would put my accounts out, wouldn’t it?

Resolution for 'bill backdated issue: 'Unapplied supplier credits' available: Yes.

The bill backdated 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 bill backdated issue yourself by looking for a resolution described in the article. If it is a complex bill backdated issue or you are unable to solve the issue, you may contact us by clicking here or by using other bill backdated support options.

For more information about resolving issues related to bill backdated in Quickbooks/QBO or to get support for the issue 'Unapplied supplier credits', click the link below: