Does anyone know how this website has done the custom subscription flow?
Webpage link here: https://www.crosbycoffee.co.uk/pages/subscribe
Or like this one: https://unionroasted.com/pages/coffeeclub-initial#part-3?1
They both appear to be using the RECHARGE Subscriptions Shopify App. You can search Shopify for more subscription apps that may fit your exact use case and the functions you need.