I am having issues with the app. Can create a customer and invoice, but as soon as I hot save it disappears for hours. Then there is no way to collect payment. New issue?

Thanks for letting us know here on this forum, Adrien. I can share information to help rectify issues you're experiencing when managing customer sales transactions.

Beforehand, are there any error messages received after saving customer invoices? Which mobile device were you using when completing this task? You can also share screenshots of your end, so I can have a clearer view of your account. Any additional details would be much appreciated.

Usually, unusual behaviors like this might have caused data damage to your QuickBooks app. We can perform troubleshooting steps to help refresh data into its default state. This process plays the same role as clearing the cache from your web browser. To do this:

iOS

1. Go to Settings and select General.
2. Under iPhone Storage, click on the QuickBooks Online app option.
3. Then, tap Offload App. This will free up the storage without deleting your app's documents and data.

Android

1. Go to Menu ☰ and select More Options ⋮.
2. From Settings, tap Refresh Data.
3. Hit YES to confirm.

In addition to that, when collecting payments from customer invoices, you'll have to create a receive payment entry to mark their invoices as paid. To learn more about this, check out this reference: Receive an invoice payment using the QuickBooks Online mobile app.

Furthermore, you may want to add specific details and personalize your sales form templates, so you can have a professional-looking form: Customize invoices on the QuickBooks Online mobile app.

If there's anything else you need further assistance with when managing customer sales transactions, just reply to this post. I'll be on this thread anytime you need additional help. Keep safe and have a great weekend ahead.