I can't add a subscription I just signed up today or the one I signed up 2 days ago because when you create a subscription, the payment date requires a future date.

Brought this up to their support and this was their response:
"this is how the system is setup to make it easy to save the reminders but that's good feedback I'm adding it to our roadmap too"

This logic make zero sense. Seems more like a bug than an expected behaviour, but apparently this is the logic of the app...