We work with a company that is both a Customer and Supplier. How do we apply their Customer Invoice to their Supplier Bill?

Welcome to the Community, @topher-activerec.

I'm here to help you apply customer invoices to supplier's bills in QuickBooks Online (QBO).

To start with, since you'll be applying your customer invoices to a bill, you'll also need to add them as a vendor. Just put a slight difference in the name, like adding a middle name, so you can save it.

Here's how to add the account:

1. Go to Settings ⚙ then select Chart of accounts.
2. Click New to create a new account.
3. Under the Account Type ▼ dropdown, tap Bank.
4. Under the Detail Type ▼ dropdown, click Cash on hand.
5. Enter the account name. (ex. Barter Bank Account)
6. Hit Save and Close.

Once done, Create an invoice and make sure we've added the information needed, especially in selecting the barter account that we created earlier in the time we manually received the payment:
 

Receive payment for the invoice

1. Select + New.
2. Hit Receive payment.
3. From the Customer ▼ dropdown, select your vendor’s (barter partner) name. Note: The details and info from the invoice you’ve created earlier will appear under Outstanding Transactions.
4. Fill in the date and amount.
5. Tap the Payment method ▼ dropdown, then Add new.
6. Enter “Barter” in the Name field, then select Save.
7. Select the Deposit to ▼ dropdown, then choose your barter bank account.
8. Click Save and close.

Then, create a bill and follow the same steps by adding details needed to this transaction pay the bill, and ensure to deposit it to the barter account.
 

1. Click + New.
2. Choose Bill.
3. From the Vendor ▼ dropdown, select your barter partner.
4. Enter all the necessary information.
5. Select Save.
    

Pay the bill
 

1. Click + New.
2. Choose Pay bills.
3. From the Payment account ▼ dropdown, select your barter bank account.
4. Select the bill you’ve created earlier.
5. Hit Make payment under Balance Due.
6. Enter the amount.
7. Click Save and close.

For more tips and details, please check out in this article: Record a barter transaction.

In your free time, you can also check out these articles. Each of them can surely help you manage your data in your book:

• Sales and customers.
• Expenses and vendors.
• Reports.

If you need additional help with managing vendors and customer transactions, please let us know. We’ll be right here to further assist. Take care, and I wish you continued success.