I have QB Plus online. Am I able to set up an automatic notice that goes to customers when their invoices are past due? Do I need to use a diff. version of QB for this?

Hello there, @katy42.

Good to see you here in QuickBooks Community. Allow me to help and guide you on how to setup Invoice reminder in QuickBooks Online (QBO). 

You can manually set up a reminder email each of your customers once their invoices are already in the past due. Let me walk you through the process: 

1. On the left menu bar, click Sales.
2. Select Customer. 
3. Double-click the name of your customer.
4. Select Transaction List.
5. Put a check mark in the invoice box, and click Batch actions drop-down arrow. 
6. Choose Send Reminders. 

You may also check this article for the other option on how to set up invoice reminders. 

If you need further assistance with the steps, I recommend calling our QuickBooks Online Support Team. They have additional tools to pull up your account in a secure environment and do a screen share. 

Here's how to contact our support: 

1. Go to: https://quickbooks.intuit.com/community/Getting-Started/Get-help-with-QuickBooks-Online/m-p/185932.
2. Click the contact us link. 
3. On the Search for something else tab, type-in Customer Support.
4. Click the Get Phone Number below. 

That should do it! Please know that I'm just a post away if you have any other concerns about Invoice reminder. Wishing you and your business continued success.