Stripe launched a new API 8. November. Is your Stripe API using the old or the new API for paid membership levels?
My stripe payment worked before but I can't make it work now. Below is the text from Stripe explaining what they have upgraded.
Here's a few major changes that may affect you:
The id field of invoice line items for subscriptions is no longer set to the subscription ID, but instead to a unique ID. The subscription ID is now contained in the subscription field and the subscription_item field contains the subscription item ID.
When creating or updating subscriptions, the default value of trial_from_plan is now false, meaning that a subscription will not automatically inherit a plan's trial_period_days. If a subscription is already trialing, switching to a new plan without specifying trial_from_plan will maintain the trial. We recommend setting an explicit trial per subscription instead of setting trials on plans.
The plan object attributes name and statement_descriptor have been deprecated. Plans are now linked to product objects by the product attribute on plans. The name and statement_descriptor attributes of the linked product are now used instead. An error is now returned if name or statement_descriptor are passed to POST /v1/plans.
Allows a new subscription's first full invoice to be on a future date, by specifying billing_cycle_anchor, with an optional proration up to that date.
Payouts were moved out of Transfers into their own resource. /v1/payouts now represents moving money from a Stripe account to a bank account or debit card, and /v1/transfers now represents Connect platforms moving money between Stripe accounts.
I've checked our Stripe account and it's still working via Default API (2018-02-28). As I see new API was released 2018-11-08 and it's marked as Latest. Our account doesn't use it. Looks like you need to switch your account to use DEFAULT API instead of LATEST. If you provide me (via PM) with your Stripe access info I'll try to check it.