Welcome to the Community, hvickar. Thank you for reaching out to us in this forum. The cheque won’t appear in the transaction list under the customer’s profile, since it's categorized as an expense. I'll explain more below.
Please know that entries that appear in this section, the Sales window, are those that affect the client's balance, or the amount they owe to your business. You can locate the cheque from the Expense tab instead. Here's a screenshot for your reference:

To review all customer-associated activities, including sales and expenses, you can run a Transaction List by Customer report. Here's how:
- Click Report, then choose Standard reports.
- Utilize the search field to find and open the Transaction List by Customer.
- Choose the appropriate date range in the Report period dropdown.
- Depending on your needs, customize the data.

We're always ready to assist you when handling cheques or other related tasks in QuickBooks Online. You can keep us notified in the Community whenever you need a hand by tagging us in your replies in this thread. Have a great day!