convert epoch number to readable date in html

Question

I have an issue with Stripe Invoices in my Angular App.

The payment created field is populating in Firestore as a number and not a timestamp.

Short of editing the field each time an invoice is created or paid, is there a way to convert the number to a Firestore timestamp?

I've tried in html:

{{ created.toDate() | date: 'dd/MM/yyyy HH:mm' }}

I have contacted Stripe, but they had no idea what i was asking them to fix.