LOT Polish Airlines website not only cannot deal with a "+" in an e-mail address – which, in case you're not aware, is a perfectly valid character in an e-mail address – but it also just craps out at the almost last step of booking, three screens after the e-mail address is provided.
Instead of you know, catching that when the address is provided.
Great website engineering there, LOT! Not being able to correctly handle a set of standards that had been in use for over half a century. 👀