Need Help: HTTPS Version Invalid in Google Search Console Despite HTTPS Setup

Hello professional SEOs, I'm facing an issue with no clear cause or solution. I have three new websites, all set up with HTTPS and fully configured SSL certificates. However, when I submit them to Google Search Console, I receive the message, 'The HTTPS version is invalid and may hinder the indexing process.' Currently, Google is indexing the HTTP version of the sites instead. I can't figure out the reason behind this issue, and I hope experienced SEOs can provide guidance.