Good day, Melissa.

I'm delighted to shed some light on this situation. In QuickBooks Online, applying one payment to two invoices from difference companies isn't possible.

You can split the payment between General Contracting and Lawncare. Another suggestion you can look at is using sub-customers as an alternative solution. This is a great feature if you want to track customers who are apart of a group or specific accounts for a larger company.  

Nonetheless, I highly recommend consulting your accountant. If you don't have one, QuickBooks has a service called Pro-Advisors that can assist you. Simply enter your zip code and browse through all the experts in the area and connect with them. Many even offer free consultations.

Thank you very much for your time. I look forward to working with you in the future. Have a great day!