This is not what we want you to feel and experience, @skinfxinc. I know how hard it can be when things aren't working the way we want them to be especially if it affects our business operations. No worries, I'm here to make it up to you by clearing things up so we can meet halfway and understand how these things work in QuickBooks Online.

Reiterating what my colleagues have discussed above, the option to choose which invoice you'd like to apply the credits to can be possible if we turn off the Automatically apply credits option in your Accounts and Settings. Just be sure to click on Save to save the changes then hit Done to close the page.

Now when we create a Receive payment transaction for the customer who has available credits, we can choose which invoice (whether it's the same product or not) and even opt not to use the credits. 

I can see that your staff doesn't have access to your Accounts and settings to turn off the Automatically apply credits option, however, it's our only way to be able to realize the goal. The ability of this feature when turned off and on is just working as designed.

Additionally, you're able to email and print multiple invoices and other sales forms in QBO. This way, you're able to save time and effectively monitor your sales transactions. You can learn more about this through this article: Email or print multiple invoices and sales forms.

I apologize for any inconvenience this has caused you and appreciate your patience we continue to work towards bringing the best experience to our customers. If you have further questions about applying credits to invoices in QuickBooks Online, please feel free to leave a comment below. We'll be here to assist you. Keep safe.