Installing on your web server

You have the certificate and the key; what remains is telling the server about them. The mistake that costs the most time is the same everywhere: sending the leaf certificate without its intermediates. Your own browser hides it — it caches intermediates from other sites — so the site looks fine to you and broken to everyone else.

Almost every server wants the same input, a fullchain file: the leaf first, then each intermediate, in order. The root is never included, because clients already have it.