Custom Fields & Email Templates, can't get it working

I have the following custom fields for invoices:

and I want to use these fields in the email templates. I can see that there is $custom1 and $custom2, but neither of these seem to work. There also seems to be 4 custom field options…so where is $custom3 and $custom4? Are these variables for something else?

How can I use my custom fields in email templates?

The app is only showing the 1 and 2 variables because they’re the only ones configured.

@david can you please advise if the variable is correct?

Okay, but why don’t they appear on the invoice template?

The variable does not seem to display what I have input in the custom field on the invoice.

Screenshot 2022-06-04 102851

here are all the available fields.