How do I send a payment to a vendor through QB?

Let me share the options to pay your vendor using Bill Pay in QuickBooks Online, Jun.

In QuickBooks Bill Pay, you have two options to choose on how to pay your vendor. The first is through ACH, and the second is through check. 

In your case, I suggest using a printed check since you don't have the vendor's banking information.

Schedule a bill payment with QuickBooks Bill Pay: 

1. In your QBO, select Expenses, then select the existing Bill if you have one, otherwise, create a new one.
2. Select Schedule Payment or Save and Schedule Payment 
3. If you create a new bill, select the option to schedule the bill right away by clicking Save and Schedule Payment.
4. To schedule payments for any existing bills, you can directly do it from the Expenses, Vendors, or Bills section.
5. Choose the bank account you want to use. You can add a new bank account or select from your connected banks.
6. If you choose to Add a bank account:
   • Find and select your bank.
• Enter your account's user ID and password, and we'll connect it immediately. 
7. In the Payment account in the QuickBooks dropdown ▼, select the corresponding account from your QuickBooks Chart of accounts to sync your payment information accurately in your QuickBooks Online account.
8. Select + Add new to create a new account in QuickBooks to track your bill payment information and click Next. 
9. Choose which payment method your payee prefers and complete the required fields. (Bank transfer (ACH): You’re required to enter the payee’s bank account number and routing number. Print check: You’re required to enter the payee’s address. The memo field is optional.)
   On this step, we need to ensure selecting Print check. Since you don't have your vendor's bank information.
   
10. Review the payment instructions, then if everything looks correct, select Schedule payment. If you need to fix anything, select Back. If you decide not to schedule this payment, you can select Cancel.

Additionally, I've added this article for you to check how to automatically match Bill Pay transactions in QuickBooks Online: Automatically match QuickBooks Online product transactions.

You can always reach out if you need further assistance with your QuickBooks Bill Pay or any QuickBooks-related concerns.