Other option to try!

From the home page screen > create + sign > customers > estimate

Estimate form will open. Go to upper left corner (little clock icon). Locate Estimate you like to convert to Invoice. In case, it’s on that list click “more” link at the bottom

Choose “Copy […]

Resolution for 'based estimate issue: 'I can’t create invoice based on estimate.' available: Yes.

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

For more information about resolving issues related to based estimate in Quickbooks/QBO or to get support for the issue 'I can’t create invoice based on estimate.', click the link below: