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

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

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