I do not know this specific domain and had not means of communication so that I would learn it more.
That's the reason domain is inaccurate and aggregate may be improper.

I did not know a port schema beforehand, the only thing I got is ports.json file,
and it is not possible to be sure about the contract so the state of api package reflects my current understanding of it

I think of this project as of a prototype or PoC and I do not use TDD for this kind of work.
IMHO, TDD can be done only if business requirements are clear - and for me they are not.

Questions:

What should we do when there is some error during port sending?
What is the contract of a port (like these in ports.json)?
What is a business relation between different entities (normally, I would just sit and ask some business person)?