A £0 Invoice does not automatically send a receipt, even if you have automatic email receipts enabled in your account settings. Stripe does not send a receipt if a charge has not been made.

This behaviour also applies to Invoices where the total amount due does not meet the minimum allowed charge for the Invoice's currency. When an Invoice does not meet the minimum charge per currency, it is marked as automatically paid and the owed amount is added to the Customer's credit balance. No email receipt is sent.

It is possible for you to send receipts for £0 Invoices by triggering them manually through the Dashboard or by customising your integration to send the email receipt yourself (without using Stripe receipts).

Note that if the Invoice has collection_method: send_invoice, Stripe sends an email to the associated Customer with payment instructions. These emails will have different subject lines than the receipt emails and will not include a receipt number.