Hi, Can anyone tell me the best way to send invoices and when they are paid, they are automatically assigned as paid in quickbooks?

Welcome to Community, Wizorian.

I can show you how to send an invoice for your customer to pay online.

Your customer can pay for their invoice with a debit or credit card if they've set up the Accept Card Payments with the PayPal app. They can also use their PayPal Wallet to pay.

Let me show you on how to send the invoice:

1. Click + New in the top right corner. then choose Invoice. 
2. Tick Accept Card Payments with PayPal at the top of the invoice,
3.  Enter all of the necessary info in the invoice.
4. Click Save and send.
5. Review the invoice. You can add any additional information to the subject line and body of the email.
6. Once done, click Send and close.

When your customer pays, you'll receive an email notification, and the payment will be recorded in QuickBooks Online.

I've got an article for you that provides additional details on letting your customers pay online: Take and process payments in QuickBooks Online.

Please know that you can always get back to this post if you have any other questions about managing your invoice payment. I'll be more than happy to help you again. Keep safe!

@Wizorian 

What kind of business do you run? A service company?