Is anyone else struggling to get the app to work on an iPhone when it’s previously been fine?

Thank you for bringing this to our attention, @justsoplumbing. Let’s sort out this matter together to get you back to business seamlessly.

To resolve this kind of concern, kindly make sure that your iPhone is up-to-date.

If the same issue persists, I suggest clearing app data of your QuickBooks Online (QBO) Mobile app. Stored cache can cause unexpected behavior while using the application. You can follow the steps outlined below:

For QuickBooks Online app:

1. Select the menu at the top right and then choose Help & Feedback. 
2. Then select Refresh Data 
3. Click Refresh.

In your Phone Settings:

1. From your phone's settings, select Settings.
2. Then, click on General and choose iPhone Storage. 
3. Select an app that's taking up a lot of space. To free up the storage without deleting the documents and data for the app.
4. Select Offload App.

That should fix the issue. If you have need further assistance with QuickBooks Mobile App, you can always drop by. Stay safe!