Hi there, @kate27.
Being able to make expenses and items billable isn't available in QuickBooks Online Essentials. This is why you're unable to split them. The said option is only applicable to the Plus and Advanced plans.
In this case, you'll need to create a separate transaction for each bill and expense to keep your records accurate.
If you wish to have this feature again, you can switch back to your Plus subscription.
I'm adding here some links about the features and reports that are included on your subscription for reference:
You've got me here to help if there's anything else you need. I'd be pleased to assist you. Thanks for coming, and have a good one!