Always wild to find a completely broken UX in core user journeys for huge tech products. 

Recent example was having a credit card expire linked to Spotify. Received a single warning email before account was abruptly canceled; this then removed access to all family plan members. In the 2-3 days before and after, there was zero email marketing to warn or win me back. When I fixed the card, I needed to re-add every account member from scratch, so just downgraded the plan. 

Fixing this flow alone would likely save hundreds of thousands or millions of accounts annually from churning.

+1, was surprised getting started with accepting credit card payments with Stripe yesterday. It wouldn't let me click the confirm button after filling out my info. No error message and checked all info was filled. Contacted customer support and after 30 min of chatting with them they directed me to another page outside of the flow to enter more info. Was surprised they didn't just link me there / build that flow within or at least present some error message that I could self service or contact customer support