I want to know how to write off a few invoices in a customer's transactions but not the customer.

Good evening, @paulrusso75. 

I'm so glad you came to the Community with your question about writing off invoices. Allow me to give you some insight about how to write these off. 

When invoices you send in QuickBooks become uncollectible, you need to record them as a bad debt and write them off. This ensures your accounts receivable and net income stay up-to-date. 

Here's how to do so: 

1. Check your aging accounts receivable
2. Create a bad debts expense account
3. Add a bed debt item
4. Create a credit memo for the bad debt
5. Apply the credit memo to the invoice
6. Run a bad debts report

For detailed instructions on how to do the actions above, check out this guide: Write off bad debt in QuickBooks Online. 

Reach back out to the Community with any other questions you may have. If you run into any trouble along the way, just make your way back here. I'm only a comment away. Have a great day!