Is there a way to prevent customers from making partial payments?

Hi there, @theonlypoolservi.

QuickBooks Online doesn't have an option to make the customer pay in full. You may have to talk to them about the terms of the invoice payment. If they have an upcoming due you can send them Statements so that they will be notified.
 

Here's how to do that:

1. Click on the + New button and select Statement.
2. Select the Statement available tab and check the box beside the customers you want to send statements to.
3. Click Save and Send. This is how it looks like:

You can also customize the statements. For more information, you can check out this article: Create and send customer statements in QuickBooks Online. 

I've added this article for your future reference in case you want to track specific aspects in your business: Run reports in QuickBooks Online. 

I'll be here if you have other questions or concerns. Let me know in the comment section below. Take care.

Personally, I would take ANY payment a customer wants to make!  I do understand your expectation of having payment in full.  The best way to encourage this is with a business practice not a system feature.

The business practice would involve a notice on your invoice which stipulates a service charge for partial payments (you can decide how much that charge should be).  If a customer pays a partial amount, you could apply the service charge and send them a statement.  The customer will catch on quickly.  Be sure to warn them in advance to meet full disclosure practices and make sure this is lawful in your part of the country.

Best,

Kevin