ok, then something in the theme is outputting content when it should not.
in 99.9 % of the cases this is because some file starts with [something here]<?php instead of just <?php
(i.e an additional space or linebreak, or any other character before the <?....
– there should never be anything before the opening php )

i would suggest you check your functions.php (theme and/or child theme) first of all and in particular any modifications you have made yourself to any (child)theme files

and your issue is probably here

[05-Feb-2020 15:14:17 UTC] PHP Warning: session_start(): Cannot start session when headers already sent in ……./wp-content/plugins/wppizza-delivery-by-postcode/v3x.php on line 1603

i.e. you are outputting stuff in ajax requests (by another plugin) which will make sessions not work
such as
…The each() function is deprecated. …
etc etc

the plugin authors should of course fix this, but – as stated – simply do not output but log error messages to bypass these kind of problems

back to the issue at hand

a) please update your plugins (especially the main wppizza plugin – what you are using is almost a year old, even though i do not think this is the problem)
b)please enable debug like so : https://docs.wp-pizza.com/troubleshooting/

ok
(you should definitely check your browser console and make sure that your php sessions are working)

without – at least – a link to the site (and better still, screenshots of your plugin settings too) i cannot really say anything

>Or is there simply no other possibility because the confirmation will “take 2 business days but can take up to 14 days (to confirm the success or failure of a payment)”?

that is exactly it. unless the payment is confirmed by the bank, it will not show up as paid.
there’s nothing the plugin can do. this is the bank(s) taking up to 14 days to confirm.
personally – for precisely that reason – i would never use sofort (unless your business is something where it does not matter too much if it takes 14 days for payments to be received.. but only you can decide that )

one thing though : if it does NEVER complete in the system , then that’s usually because the required webhook is not set-up in the live account (this does not seem to be the case from what you are saying, so am only mentioning it here for completeness sake)

you should look at the minicart options here
wp-admin/edit.php?post_type=wppizza&page=layout

maybe attach the minicart to a different element (“Append to element”) instead of the default body element
as you have a number of static elements on your page you might also need to adjust some padding/margins on those
kind of all depends on where exactly you want to display this .i.e what you want to display topmost etc etc

Good stuff.
happy to hear it. I’ll make that part of the next wppizza update.

Thanks for letting me know / testing the fix

Did you set the webhook in your Stripe account as described in the plugin (gateway) settings ?

i’m a bit confused now
if I go here:
https://www.[yoursite].it/wp-admin/plugins.php
i get different languages in the descriptions (quite probably because the plugins and their descriptions have no IT translation)
even though WPPizza is DE-activated ???
So i assume you are not actually referring to this ?!

if i look at my clone of your site here now i get the same plugins names/descriptions (/wp-admin/plugins.php) as well as the same admin labelling – i.e the stuff on the left like “Media”, “Pagine”, “Prodotti” “Openig Hours” etc etc (/wp-admin)
regardless of whether wppizza is active or not (i can show you screenshots if you like)

i must be missing something…:(
please can you give me a distinct example (some text/heading/label somewhere) that changes/is different
depending on whether wppizza is activated or not ….