Let's do some troubleshooting to record your expenses, @sb_mms.
You can close and restart the app to fix the run-time system glitches that ceased you to enter expenses.
Also, you can clear the app data stored in the phone's memory to cache new working data.
Here's how:
For Android
From your device's Settings⚙, select Apps (varies by device), choose QuickBooks app from the list and then select Storage. Finally, select clear data.
For iOS
From your phone's Settings⚙, select Setting General iPhone Storage and choose an app that's taking up a lot of space. To free up the storage without deleting the documents and data for the app, select Offload App.
Alternatively while using the app:
Android: From the More Options symbol ( ⋮ ), select Settings, then select Refresh Data, and then choose Yes.
iOS: From the Menu ☰, select Help & Feedback, select Refresh Data, and then select Refresh.