How can I add a "quantity" field to a form that pops up whenever an item(s) is checked?

I am building a product reorder form, and have each product formatted as a text field with a checkbox.

Should I create a "quantity" number field and apply some sort of conditional formatting to bring an instance of that number field up after each product box is checked? If so, how?

Unfortunately, this is not something that can be easily done due to the way how the form layout works.

You might consider using a Purchase Order tool from Payment Fields instead, where you can add the product quantities as custom inputs or drop downs.

Example with custom input quantity options:

See the next guide for more information:

How to Add Options to Payment Forms?

If you need any further assistance, please let us know.