A free app is not free of cost. It costs page weight, a dependency and a ceiling you will meet at
Free tiers are metered on something — orders, views, products, features — and which meter applies decides when you are forced to upgrade.
The subscription is rarely the largest cost; page weight and dependency usually are, and neither appears on an invoice.
A free app that becomes essential is a paid app with a delay, so read the ceiling before building a workflow on it.
Genuinely free apps exist, usually from vendors monetising elsewhere — that is fine, provided you know what the arrangement is.
Free of subscription, generally not free of cost. They add page weight to templates that convert, create a dependency on a vendor, and frequently carry a ceiling you will
The full guide has the formats, the deadlines and the worked examples.