This can happen when the customer reaches the payment page, but then
returns back to the booking form via the back button: the browser
remembers the URI with the cart slug, trying to make it ready, and then
it fails because it is already pending.
I did not like the idea of modifying a payment that is already not
a draft, because it seems to me that can lead to errors if we receive
Redsys notifications of payments that are being changed back to draft.
In fact, i believe that draft payments maybe should go to a different
relation altogether, so that i can prevent UPDATE on payment by guests,
but maybe i am going overboard now.
jordi fita mas
7e39e5f549