Accountant app not opening on iphone

I understand how relevant it is for you to manage your business, Walkman. Let's perform some troubleshooting steps to help rectify issues with the app.
 
Sometimes, unusual behaviors like this have caused data damage or stored cached files in your QuickBooks app. Let's reset the app data to refresh your device and set it to its default state. To guide you with the troubleshooting steps, refer to these steps:
 
For iOS
 

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

For Android
 

1. Go to the Menu ☰ icon and tap More Options ⋮.
2. Click on Settings, then Refresh Data.
3. Select YES to confirm.

Once done, re-open the app and log back into your account. Here’s an article that will guide you on how to get the most up-to-date information in the program: See your latest data in the app.
 
However, if the same thing happens, I recommend using the web browser available on your mobile device. This way, you can efficiently continue managing your invoices.
 
I'll also include this reference to help you uninstall and reinstall the app in case the issue persists: How to Download the QuickBooks Online Mobile App.
 
You can reply in the comments below if you require additional assistance managing tasks in your account. Stay safe.