For reasons which I will discuss later this week, I decided to skip my return flight to Frankfurt on Ryanair and book with Lufthansa instead.
The LH fare itself wasn't bad, but booking it turned out to be a huge pain. LH levies a €10-15 booking fee on most flights booked through its website which can be avoided by paying with PayPal. Naturally, I attempted to use my PayPal account, but encountered the following error message:
My PayPal information was entered correctly--LH's website just wasn't accepting it. So I booked with expedia.de instead. Their booking fee was only a couple Euros and at least I'll earn about 300 credit card miles for the transaction.
People always attack United Airlines' website as being buggy and error-prone, and it is, but it was oddly refreshing to see that even the carrier oft-heralded as the airline archetype isn't immune from error messages--and cannot even spell out those error messages in a grammatically correct form!