Without this certificate, you will not be able to register.
The CVEC is "intended to promote the social, health, cultural and sporting welcome and support of students, and to bolster the preventive and health education actions carried out for them" (article L. 841-5 of the Education Code).
By law, it is collected by the CROUS. With an annual fee of €95, you may or may not be subject to it, and in certain situations you may be exempt.
Paying the CVEC is a compulsory part of enrolling in higher education.
To simplify your CVEC contribution, you can do it online at https://cvec.etudiant.gouv.fr/. It is compulsory to present it when you register, and it will also give you access to Crous scholarships and residence accommodation. Note that Crous residences allow you to reduce your monthly expenses, but you still have to pay for the day-to-day costs of your accommodation. elec prices for electricity rates in France.