Being able to have this Grammarly compatibility feature on sales forms would really help your business, scottnadeau.
You'll want to let our product team know how this will benefit your business needs. You can visit our Customer Feedback page by clicking the Give Feedback option so you can send your request. I've provided a screenshot for your guide:

Additionally, you'll have to record the payment from your customer and mark them as paid. Otherwise, the invoice is left open and unpaid. To learn more, I've added this article for more details: Record Invoice Payments In QuickBooks Online.
Reach out to us if there's anything else you need when creating your sales forms. We'll always be right here to help you if you need further assistance.