just to narrow things down: are you using inline payments or redirect payments in stripe ?

did you disable
“Apply above position to all print/email templates. Disable to set position/display on a per email/print template basis”
? (both plugins)

if you did , did you then enable it in the templates ?

i *might* be the case that you simply have some parameters not set /saved (i believe you had some “fatal error- out of memory” messages in your logs)

so i would suggest (short of reinstalling everything of course)
you go through all the wppizza admin pages (sizes, settings, gateways etc etc ) as well as all your wppizza plugin pages (add ingredients-> options, add ingredients-> settings etc, delivery by postcode options/settings etc etc – you get the idea)
and just save them once so we know you have no “missing” parameters in your db

I cannot guarantee this fixes it, but certainly worth to make sure the problem is not there (should only take 5 minutes to do really)

simply ignoring “session_start(): Cannot start session..” is not a good idea . might work seemingly but you will probably end up with issues at some other point
also, fixing this will most likely also fix all other warnings/notices you have there , as they are most likely related

if everything fails, make/send me a duplicator package (put it somewhere i can download it or – if that works for you – simply give me admin access to your site i can do this myself)
(https://wordpress.org/plugins/duplicator/)
and i can install a clone here and see what the outcome is in my scenario

Sorry, but there are no plans for this to be implemented (at least by myself) in the near or even medium term future.

PS: I had quick look at the sofort account . they now have/display an actual “API Key” – which they did not before.

So – for clarity – it is actually *not* the API Key you should enter into the “Gateway Project API Key” in the wppizza gateway settings, but what they call the “Configuration key for your shop system”

which is in fact a combination of
Customer number:Project ID:API key

Hope that helps

– what version of wppizza did you update from please (if you remember)
– can you enable debug like so https://docs.wp-pizza.com/troubleshooting/ please and tell me what your debug log says ?
– please also re-save your permalinks (WordPress -> Settings -> permalinks ) especially if you have changed some related settings somewhere

lol.
I don’t actually think i will ever get any ROI on this , given the development time that was involved (and I dont think this will be particularly popular, though I might be proven wrong), but your post made me curious as to if this would be possible to do to start off with and might open up other – as yet unknown – possibilities in the future.
So there you go :)
As it’s – evidently – quite new , i’m happy to hear any suggestions (or indeed any problems you may have of course).
Though am not committing to add to what’s there as it stands, feel free to suggest things . Will all somewhat depend on simplicity of implementation etc

Cheers