Okay so one immediate issue I see security-wise though is you're sending security key passwords over email … and from what I gather in your docs, only over email? Either way sending it over email sounds shaky at best.
QOL request: on the institutions page (https://developers.belvo.co/docs/institution), can you add links to the bank sites in question?
I like that you have a postman collection at the ready in your docs, that's nice.
Also your homepage is just … I don't think it's good. Sorry, I know this is probably not useful feedback, but it's a nearly autogenerated landing page for the docs site, it doesn't inspire confidence. I want you guys to succeed so please spend some money on a fresh new homepage if you're not doing that already.
Good luck!!