When adding new payees, our assistant incorreclty classified vendors as customers. Can I change a customer to a vendor or do I need to go into each transaction to change?

I appreciate you sharing your query here with us, stavrue2020-. I've got insights to share when handling customer sales and vendor expense transactions in QuickBooks Online.

In QuickBooks, vendors are people or companies that you owe money to or subcontractors that work for you. Customers on the other hand are individuals or businesses who buy products and services (i.e. items) from a business, so you can quickly associate them with invoices, sales receipts, and other sales forms. Thus, these transactions differ from each other.

That said, it's best to handle these concerns beforehand to make sure balances in your account aren't mixed up. You can inactivate this customer to remove them from the lists and menus in your file and delete all transactions associated with this client. Doing so will help your books stay accurate. 

To make this customer inactive:

1. Go to Sales, then select Customers.
2. Select the customer's name to open their profile.
3. Click on the dropdown ▼ next to Edit.
4. Then, choose Make inactive. Then confirm by selecting Yes, make inactive.

To delete the transactions linked to this customer:

1. Go to Sales, then select All Sales.
2. Find the invoice that you want to void or delete.
3. In the Action column, click the dropdown ▼, then select Void or Delete.

In addition, you may need to re-create all the customer-side entries to a vendor-side transaction. This may be a long process for you. However, I recommend consulting your financial professional to provide additional guidance in handling these records.

Moreover, here's how to create a profile for a vendor:

1. Go to Expenses and select Vendors.
2. Select New vendor.
3. Complete the fields in the Vendor information window.
4. Then, select Save.

Furthermore, you can utilize this guide to get a report on all money paid to a vendor: Run a report with vendor total.

I'll keep an eye on this thread if there's anything else you need assistance with when managing vendors in your account. Let me know any time below, so I can provide additional help. Keep safe and have a good one!