Like many online businesses, we're preparing to support Strong Customer Authentication (SCA). In a nutshell, it means we'll need to support a new 3D secure verification step during the payment process. Payments can also be challenged 'off session' (i.e. when people aren't using the app).
Billing and it's associated edge cases are some of the most complex pieces of Boords. They also come with the most stress, being where the rubber meets the road business-wise. I built the previous version of our billing system on my own. The experience was... not great. There was a fair amount of (self-inflicted) pressure to get it right, and the added stress of not having experience building a billing system.
This time, there are two of us working on it, which improves the experience immeasurably. I think the main value is having to articulate the changes we need to make. Working on your own, it's all too easy to plough ahead with some opaque strategy, only to find it doesn't pan out at all, then just fumble around for a while before calling it a day and trying again tomorrow. Accountability demands we are more methodical. Or at least limit the fumbling.