There are a lot of people out there who like iPhone hardware and software, but don't like the way Apple locks them inside the App Store walled garden. For these folks, the alternative to the App Store was to jailbreak their iPhone and then use the third-party Cydia app store that provided both free and paid apps.
The apps on the Cydia store that sold for a fee used PayPal for payments. Cydia founder Jay "Saurik" Freeman announced on Reddit that the Cydia app store was shutting down its payment system. He went so far as to say that he wanted to shut down the entire Cydia Store before the end of the year.
I have to recommend that everyone removes their saved paypal info from their cydia account until further notice.— Andrew Wiik (@Andywiik) December 13, 2018
The reason payments ended early had to do with an integration issue between PayPal and the Cydia store. The integration issue, according to a Tweet by Andrew Wiik, had to do with a flaw that could result in the account owner being charged for purchases on the Cydia store without their approval. At the time that was announced, it was also said that no user data was at risk.
Saurik has stated that the decision to eliminate the purchase option at the Cydia store had nothing to do with Apple or its infamous legal machine. According to Saurik, the Cydia service was just not profitable, and he says he had no passion for maintaining it. He stated, "...it came at great cost to my sanity and led lots of people to irrationally hate me due to what amounted to a purposeful misunderstanding of how profit vs. revenue works." For now, the Cydia store will continue to offer free apps for download. A post talking about the future of Cydia is promised in the coming days.