Read one company of your school by its Edusign ID. An unknown ID answers 404 COMPANY_NOT_FOUND.

Several learners and external contacts can be attached to one company, and a change to the company applies to all of them.

Attach a learner with companyId on PATCH /students/{id} (or its by-reference-id twin): it is the "Company" field of the learner record in the School app. That call also copies the company display name into the learner's historical company text; updating the company later does not rewrite that text.