When a new project is created, the deployment protection is set to enabled with standard settings. The deployment protection usually does not apply to production or custom domains. However, it seems like that Vercel is accessing a different domain it assigned to the deployment, which then required Vercel authentication, causing a 403 error when creating the deployment preview image.
I have create a new account on vercel, then used the repository template mdexpress to create a blog. The logs show access to mdxpress-9gdi9q0z9-me-5632s-projects.vercel.app after deployment. This page requires authentication, I assume that Vercel is using this domain to create the deployment preview?
Could it be related to the deployment protection settings?
I have seen multiple reports about this on reddit and people don’t know how to solve it. As said, this is a new vercel account with default settings, and the mdxpress template as deployment.