The billing of "free" domain and invoice generation

[NickoLabs]

Greetings

I hesitated to post here instead of going to Support, but I recon it is working as intended. Therefore, I might actually need some help in better configuring my WHMCS setup. Let me explain the situation and the expected results first.

So the last couple months, we added our clients to a new WHMCS system. Our hosting provide a free domain.
So we first added our client, then synced their hosting cPanel products and finally added their domain names.
Basically creating active domain name orders that would be free when adding them.
Finally, we switched the Due Date of all hosting and domain names to a specific date. Invoices were generated this morning as per our automation.

Alas, the clients are getting an invoice for the domain name at 0$, then a notification that this invoice is paid, and also another invoice for the hosting that they need to pay.
It's creating a lot of confusion and a TON of phone calls since all those invoices were generated on the same day (oof).

So my questions is : Is there a way to MERGE hosting and free domain invoices, even if they are basically two different "orders"?

Non of the clients have the "Seperate Invoices" setting checked.

Is my situation explained properly? Is there something I can do, improve, in order to minimize email counts and confusion in the future?

[NickoLabs]

I will reply to that, as I did manage to sort most of this issue out.

The due date of both domains and products must be the same AND
the payment method of both domains and products must be the same.