The "past_due" status for a subscription happens when a customer starts a subscription, but then their payment method fails when charging for the next renewal period. This means that no payment was collected and we suggest not sending the subscription product until payment succeeds.

Stripe typically retries failed payments. You can modify the retry rules in your Stripe settings panel.

You can manually retry payments in Stripe as well by clicking on the failed invoice and clicking the three dots on the right hand side and "Retry Payment".

If a payment succeeds, Monto will change the status back to Active for their subscription and you are free to send their product for that period.