Every app is also sold on the Odoo App Store at apps.odoo.com. Buy the core app and any adapters or packs you need there; the prices shown on the store include the required dependencies, so what you pay at the store checkout is the whole cost for that app.
Store purchases are licensed through the store itself - there is no license key to request or enter. Install the apps and they run fully licensed.
The Maintenance & Support subscription (updates, priority support, license portal) is not sold on the store. Store customers can add it separately at shop.latasys.app/subscribe for GBP 29/month.