Is it legal to use non-public API (API that i figured out on my own)?

Question

I would like to know if it is legal for me to collect data from some 3rd party service via their api?

This is a situation: I have customer, Customer uses some system that provides them reports. Customer wants me to have access to those reports so they give me their credentials and i'm using my service rest-api calls using customer's credentials converting their data from that system rest api to my DB that I share only with this customer per his request.

Is it ok thing to do?

I am concern because it gets deeper. I have many customers who are using the same service that i figured out api to and willing to collect data

Answer 1

Ask them, or read their legal contracts with you and licensing terms of their API. Consult law of the land too.

Nobody is going to read this question after I would like to know if it is legal...

And Oh, delete the question before you get 50 down-votes because it just doesn't belong to this forum :)