How do you make a sub client in QuickBooks mobile app?

It's good to see you posting in the Community, Illuminate. I can share some information on creating a sub-customer in QuickBooks Online mobile app.

The feature to add sub-customers is unavailable using the QuickBooks mobile app at the moment. However, we can open your account using the regular browser and add your sub-customers there. Follow the steps below:

1. Go to ​Sales. Then select Customers.
2. Click New Customer.
3. Enter the sub-customer’s name and contact info.
4. Select the Is a sub-customer checkbox. This action will display a parent customer dropdown menu.
5. In the Parent customer ▼dropdown, select the parent account. 
6. Select the Bill parent checkbox if you want to bill the sub-customer with the parent customer. Leave this unchecked if you want to bill the sub-customer themselves.
7. Review each section and enter any info you need for the sub-customer then Select Save.

You can also refer to these articles for additional reference on this topic:

• Add and manage customers in QuickBooks Online.
• Compare mobile app features.

For future reference, visit this article if you want QuickBooks to automatically process your customer payments and categorize them into the correct accounts: Record invoice payments in QuickBooks Online.

If you have more questions on adding sub-customers or QuickBooks in general, feel free to reply in the comments. I'll get back to you as soon as I can. Stay safe.