How tf do I explain my manager that I simply can't change the damn response coming from a 3rd party API without hurting his fragile ego but while also using crayons.

The best part is that I'm working on the frontend.

Tell him you'll need a data science team with an engineer to craft an ETL data Lake with machine learning on the block chain

the last part had me dead

If someone will not hear about problems in their plan to safeguard their ego, that someone is not a manager, but a boss.

If someone who is not your boss is responsible for hiring this vendor, tell him to blame that person. Insecure-dick bosses love to kneecap each other.

If the person who hired the vendor is your boss, say the vendor is not fulfilling the contract. It's a disguised way of saying "boss, you are not responsible for hiring a lemon, they said they were better! they are at a fault, not you".

Conclusion: your boss' parents did a terrible job of teaching him responsibility. Start planning your exit.