What do “custom domain” and “alias” mean in Vercel? Are they the same thing?

I am assigning an alias to the release branch using the Vercel API, specifically example.com. Additionally, I have configured the Vercel domain settings for the preview environment and the release branch.

In this scenario, I am unable to assign an alias from the GitHub Actions workflow. The alias is being assigned using the Vercel API as documented here: Vercel API – Assign an Alias.

Could the issue be that the domain is already configured in Vercel, causing a conflict when attempting to assign the alias via the workflow?

I have attempted to assign the alias using the Vercel API. My expectation is for the release aliases to be assigned through the workflow.