I'll make sure you're able to record your business expenses accordingly in QuickBooks Online (QBO), @Angela C.
Based on your scenario, yes, you can book the advanced check as a business expense. You'll first need to add the employee as a vendor (i.e., [Employee] Company Advanced). Then, treat the difference (check written by the employee) as a reimbursement. This way, you can keep your financial data accurate.
When you're done adding an employee as a vendor, you can create the advanced check by following these steps:
- Go to the + New button.
- Select Check.
- Choose the Payee from the drop-down.
- From the Bank account drop-down, select the account the check withdraws money from.
- Complete the check fields you need.
- Select the Print check option if you want to open the check queue to print now. Or select the Print later checkbox if you want to print the check later.
- Select Save and close to close the check window.

Once the employee writes the check to the company for the difference, you'll have to record it as a reimbursement. For the step-by-step guide, you can refer to this article: Enter a refund from a vendor.
Then, I'd recommend pulling up the Check Detail report. This way, you can verify that the checks you've written are recorded appropriately. To do this, go to the Expenses and vendors section from the Reports menu's Standard tab.
In keeping with this, I'm also adding this article to further guide you in managing your expenses and vendor accounts in QBO: QuickBooks Help Articles for Expenses and Vendors. It includes topics about paying expenses, managing inventory, and purchase orders, to name a few.
Please don't hesitate to let me know if you have other concerns about managing business expenses in QBO. You can drop a comment below, and I'll gladly help. Take care, and I wish you continued success, @Angela C.