I see how useful it would be to have the progress invoicing feature on your end and recognize your effort in contacting our live support, @bobrrc. 

Currently, the updated QuickBooks Online (QBO) invoice doesn't support progress invoicing. However, if you're using the old one, I'd like to know if you encounter any error messages.

On top of that, since you mentioned that you migrated from QuickBooks Desktop (QBDT) to QBO, please know the estimates used for progress invoicing won't link to the invoices you created in QBDT. You can read more of this here: Learn how features and data move from QuickBooks Desktop to QuickBooks Online.

For future reference, you might want to send reminders to your customers about their invoices due automatically, check this article: Send invoice reminders automatically or manually in QuickBooks Online.

Feel free to return here if you have additional questions about managing your invoices. I'll be willing to help. Keep safe.