The partnership agreements are not mandatory but are strongly recommended - see Guide for Applicants:
It is also strongly encouraged to conclude a Partnership Agreementt with the TC
partner organisations to determine clear and transparent rules governing the internal
relations between MS/AC beneficiaries and TC partner organisations (e.g. use
and distribution of funding, legal issues, IPR, confidentiality, scientific responsibilities
to implement action tasks, compliance with grant agreement obligations, etc.).
The MSCA explained by your National Contact Points