Hi there marksman projects,
Thanks for reaching out about your mobile app issue. QuickBooks Online is a great tool able to help you keep track of sales and expenses so you know the profit of your business. I can point you in the right direction for assistance with this.
One cause for a tab like the customers tab not showing up in the app would be app data. To resolve this, you can try to remove the app on your device, and download it again from your mobile device’s app store.
If you have any other questions feel free to reach out here.