Can I check why when I edit an invoice but can't save by using phone

Hello there, @@grace-lim-ingrad.

QuickBooks always allow to save an invoice using a phone device. Can you share if there's an error occur when trying to save it? This surely help me to look more resources and provide accurate details of your concern. 

For now, let's clear the app's cache by following the steps below.

In your device settings:

• 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.
• iOS: From your device'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.

If the same thing happens, you'll want to uninstall and update your device first if needed and then reinstall the app to refresh the system. 

Also, you'll want to edit and save it using  a web browser. These are the supported browser's in QuickBooks:

• Google Chrome: version 78 or newer
• Mozilla Firefox: version 76 or newer Note: To preview and print forms on Mac OS, you'll also need the Firefox PDF plugin.
• Microsoft Edge: version 75 or newer
• Safari: version 12 or newer (Mac only)

If you want to personalise your sales forms, please visit these resources to get more tips:

• Customise invoices, estimates, and sales receipts 
• Add, customise, or remove logos on sales forms
   

Please let me know how it works for you, grace-lim-ingrad. Take care and stay safe.