Thanks for joining the thread, RogerM.

Aside from checking the Form numbers, we also need to make sure that you've selected the correct template. Create an invoice as usual. Click on Customise button at the bottom. Then, select your customised template. You can also follow these steps to make it default:

1. Go to Custom form styles.
2. Locate the invoice template. Click on the arrow beside the Edit.
3. Select Make default.

Let's perform these steps if what you'd like to achieve is to show the Invoice no. field when creating it. This field won't appear on the invoice page if this option isn't turned on. Though, it'll still show when previewing it since QuickBooks will automatically generate an invoice number.

1. From the Gear icon, select the Account and Settings.
2. Select the Sales tab. Click on the Sales form content section to expand it.
3. Check the Custom transaction numbers box. Then click on Save.

Also, let's check if your Adobe Reader/Acrobat is updated. It can cause errors when previewing a document if you're using an old version.  You can check this article as your guide on how to update, repair, or re-install Adobe Reader/Acrobat.

I'd suggest contacting our Customer Support Team if there are no changes. They'll be able to check the cause of it.

1. Go to Help and select Contact Us.
2. Enter "Invoice Number" as the topic. Click on Let's talk.
3. Select Start an email.

You can check this article if you need help with recording customer payment.

Hope this helps. Reply to this thread if you need further assistance from me.