So ok here it is, as asked in the comments.

Setting: customer (huge electronics chain) wants a huge migration from custom software to SAP erp, hybris commere for b2b and ... azure cloud
Timeframe: ~10 months….

My colleague and me had the glorious task to make the evaluation result of the B2B approval process (like you can only buy up till € 1000, then someone has to approve) available in the cart view, not just the end of the checkout. Well I though, easy, we have the results, just put them in the cart … hmm :-\
The whole thing is that the the storefront - called accelerator (although it should rather be called decelerator) is a 10-year old (looking) buggy interface, that promises to the customers, that it solves all their problems and just needs some minor customization. Fact is, it’s an abomination, which makes us spend 2 months in every project to „ripp it apart“ and fix/repair/rebuild major functionality (which changes every 6 months because of „updates“.

After a week of reading the scarce (aka non-existing) docs and decompiling and debugging hybris code, we found out (besides dozends of bugs) that this is not going to be easy. The domain model is fucked up - both CartModel and OrderModel extend AbstractOrderModel. Though we only need functionality that is in the AbstractOrderModel, the hybris guys decided (for an unknown reason) to use OrderModel in every single fucking method (about 30 nested calls ….). So what shall we do, we don’t have an order yet, only a cart. Fuck lets fake an order, push it through use the results and dismiss the order … good idea!? BAD IDEA (don’t ask …). So after a week or two we changed our strategy: create duplicate interface for nearly all (spring) services with changed method signatures that override the hybris beans and allow to use CartModels (which is possible, because within the super methods, they actually „cast" it to AbstractOrderModel *facepalm*).
After about 2 months (2 people full time) we have a working „prototype“. It works with the default-sample-accelerator data. Unfortunately the customer wanted to have it’s own dateset in the system (what a shock). Well you guess it … everything collapsed. The way the customer wanted to "have it working“ was just incompatible with the way hybris wants it (yeah yeah SAP, hybris is sooo customizable …). Well we basically had to rewrite everything again.
Just in case your wondering … the requirements were clear in the beginning (stick to the standard! [configuration/functinonality]). Well, then the customer found out that this is shit … and well …

So some months later, next big thing. I was appointed technical sublead (is that a word)/sub pm for the topics‚delivery service‘ (cart, delivery time calculation, u name it) and customerregistration - a reward for my great work with the b2b approval process???

Customer's office: 20+ people, mostly SAP related, a few c# guys, and drumrole .... the main (external) overall superhero ‚im the greates and ur shit‘ architect.
Aberage age 45+, me - the ‚hybris guy’ (he really just called me that all the time), age 32.
He powerpoints his „ tables" and other weird out of this world stuff on the wall, talks and talks. Everyone is in awe (or fear?). Everything he says is just bullshit and I see it in the eyes of the others. Finally the hybris guy interrups him, as he explains the overall architecture (which is just wrong) and points out how it should be (according to my docs which very more up to date. From now on he didn't just "not like" me anymore. (good first day)
I remember the looks of the other guys - they were releaved that someone pointed that out - saved the weeks of useless work ...

Instead of talking the customer's tongue he just spoke gibberish SAP … arg (common in SAP land as I had to learn the hard way).
Outcome of about (useless) 5 meetings later: we are going to blow out data from informatica to sap to azure to datahub to hybris ... hmpf needless to say its fucking super slow.
But who cares, I‘ll get my own rest endpoint that‘ll do all I need.

First try: error 500, 2. try: 20 seconds later, error message in html, content type json, a few days later the c# guy manages to deliver a kinda working still slow service, only the results are wrong, customer blames the hybris team, hmm we r just using their fucking results ...
The sap guys (customer service) just don't seem to be able to activate/configure the OOTB odata service, so I was told)
Several email rounds, meetings later, about 2 months, still no working hybris integration (all my emails with detailed checklists for every participent and deadlines were unanswered/ignored or answered with unrelated stuff). Customer pissed at us (god knows why, I tried, I really did!). So I decide to fly up there to handle it all by myself

I have this login page on my app. A user (a number of them actually) told me that they can't log in because the app tells them to "login in later". 😨

Is my button for deciding to login later so poorly designed that it looks like a message?

And the only way you can log in later is by pressing the frikin button, how does a person, with a smart phone tell me for the second time that its telling them to log in later