Can somebody explain the difference between Sales location and location in the invoice

Hi there, @PS11_2.

The Sales location is referring to the address of your customer. On the other hand, the Location feature in the invoice is for location tracking to categorize data easily by outlets, regions, or departments of the company. 

For more information about the location feature in the invoices, you can check out this article: Customise sales forms by location.

I've also added this article for your future task to help you record multiple payments to one invoice easily: Record invoice payments in QuickBooks Online. This also contains steps on how to void or delete your invoice.

You can always tag my name in the comment section below if you have other concerns or questions. I'd be happy to answer them for you. Have a beautiful day ahead.