SSL Error Subdomain. Error

I'm facing an error with my client's domain. Currently, the frontend is hosted on Vercel and configured in Cloudflare's DNS. However, the backend is hosted on a VPS and is declared in Cloudflare's DNS. But the connection between the front and back keeps giving error 525. I've already added to the Dockerfile to import the certificate for the site to work, but I still haven't had any success. Could someone give me some guidance?