you have to have billable (reinbursed) expenses turned on in company settings

in US versions that is at gear>settings>company settings>expenses>bills and expenses and turn on make expenses and items billable
check mark to track billable expenses and items as income
then in company settings>advanced>chart of accounts click the edit pencil and select the […]

Resolution for 'billable expense to a customer issue: 'how do i link a billable expense to a customer' available: Yes.

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

For more information about resolving issues related to billable expense to a customer in Quickbooks/QBO or to get support for the issue 'how do i link a billable expense to a customer', click the link below: