How do you record a payment on this new junk?

I can see that adapting to changes can be challenging, David. I'm here to help you navigate the new QuickBooks mobile app.

First, I acknowledge the unavailability of the option to send a paid receipt in the latest QuickBooks Online mobile app.

I can see the benefit of this feature for you and other customers. For now, it would be most effective to communicate your feedback directly to our Product Developers. They're genuinely interested in hearing your input and highly encourage you to share your suggestions.

To send your input, here's how:

1. Open your QuickBooks Online account.
2. Go to the Gear icon located at the top-right corner of your screen.
3.  Under the Profile section, select Feedback.
4. Type in your suggestions and then click on Next.

For now, I suggest sending the paid receipt using the browser version of QuickBooks. 

To record an invoice payment in your QuickBooks mobile app, follow these steps:

1. Go to the shortcuts menu and choose Invoices.
2. Select the Plus icon in the lower right corner.
3. In the first field choose the customer you are invoicing.
4. Next, enter the necessary information such as Date, Terms, and  Due date.
5. Go to Add products or services to add line items you will be charging to your customer.
6. Input the details in the Line item.
7. Once done entering all the information Press Save.

Furthermore, I'd also like to share this article to learn the various features supported on mobile devices: Compare mobile app features.

To keep updated on the product's latest release and updates, you can check out this article: QuickBooks Blog.  

You can always continue this thread by posting additional questions about recording payments in QBO. We're readily available to assist you every step of the way. Have a great rest of the week.