Cloned site redirects to main sites

I created a staging area on a multisite network. I had a single website, for which I added the network feature. I then created the staging : staging.defi-ecologique.com. I then cloned the main site on the subdomain, following one of your tutorials:

https://premium.wpmudev.org/blog/set-up-staging-site-cloner/

now, each time I access the subdomain backend, I get an error regarding an invalide SSL certificate and all links (when I click "visit the website" or when I edit permalinks, for instance) send me to the main site, and not the subdomain.

Credentials already sent!