I understand what you're feeling now and how important to access your account without any issue. Allow me to help sort this out for you.
To start, let's make sure that the app's O'S version is 9.3 or later to get the latest updates. This way, the mobile device is up to date to its most recent operating system version.
To check for an update on a supported Apple device:
Go to Settings. Ensure your device is connected to a power source.
Click on Software Update.
The iOS will automatically check for available updates.
Also, we can clear the cache of the mobile app to eliminate the accumulated junk files. You'll have to select Setting General iPhone Storage and choose QuickBooks Online. Then, tap the Offload App. For more details, see the third step through this article: Troubleshooting Quick-Start Guide For The QBO App.
However, if the issue persists, I recommend uninstalling and reinstalling the mobile app. It helps boost the app's performance since it'll have a clean slate.
You can also access your company via the browser as a workaround in case you want to pay your account in QuickBooks.
I've added our QuickBooks Support page. It contains articles, video tutorials, and more that'll guide you in managing your QuickBooks account.
Should you need additional help in completing your task with QuickBooks, you can always find me here. Have a good one.