You can send it via email and then see if they viewed it from the customer page screen (you may have to edit the view to add that column)

You can also see a bunch of details in the more>audit details of the transaction.  It should show you when it was sent.

Resolution for 'audit details issue: 'Why do I have to write my question in less than 170 words? There are issues with the Estimate feature.' available: Yes.

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

For more information about resolving issues related to audit details in Quickbooks/QBO or to get support for the issue 'Why do I have to write my question in less than 170 words? There are issues with the Estimate feature.', click the link below: