Not sure if this rough draft is useful. It’s what I was thinking in general.

Invoices

amount_sat

created_at

paid_at

web_session_id (linked to cookies?)
expires_at
plan_id

offer_id

external_invoice_id

external_shop_id

(Does invoice payment trigger a subscription update?)

subscriptions (MAX: one per identity id?)

identity_id
expires_at

plan_id

(latest_paid_invoice_id?)

Offers

Name

Description

Period

amount_sats

plan_id

expired_at (no longer available)

Plans

Name

Description

(Basically feature sets)