“So, should I book the expense under inter company loan (due from) or should I book the expense and bill back?”

You can do Both.

You post that cost NOT as your expense, but to Other Asset (your loan to them). You mark it billable to them as a customer […]

Resolution for 'Company Loan issue: 'When to use Inter Company Loan account VS Bill Back?' available: Yes.

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

For more information about resolving issues related to Company Loan in Quickbooks/QBO or to get support for the issue 'When to use Inter Company Loan account VS Bill Back?', click the link below: