How do I associate an expense (or deposit) with a particular customer? How do I earmark lumber I bought today for Smith and lumber I bought yesterday for Jones?

Hello there, owner-loveonrail.

I'm providing additional details about associating expenses or deposits in a specific customer in QuickBooks Online.

You need to turn on the Track expenses and items by customer and Make expenses and items billable features from the settings. Doing this will generate customers when creating an expense in the system. Please note that these options are only available in QuickBooks Online Plus and Advanced. 

Here's how:

1. Go to the Gear icon and select Account and settings.
2. In the Advanced tab, turn on the Track expenses and items by customer and Make expenses and items billable features.
3. Click Save. Then, Done to reflect the changes.

For further guidance, you can visit this article: Enter billable expenses. Once done, you can follow the steps shared by my colleague above.

Other features aren't available on iPad. I'd recommend using this article to learn which features are available on supported devices: Compare mobile app features.

Please let me know if you have more concerns about entering customers on transactions and other tasks related to QuickBooks Online. Take care and stay safe.