I tried both the OwnTracks server and Dawarich, and had problems using them with my reverse proxy (Caddy), which I didn’t manage to fix. Eventually, I installed the Nextcloud app Phonetrack, and I’ve been using it for months with the OwnTracks client: it works fine, it can also export GPX files, which I can use to tag pictures shot with my camera, using Darktable. I recommend this solution if you are already using Nextcloud!