This how you put it in mcgalaxy
https://www.classicube.net/forum/viewpost/10055-bserver_texture_pack/
But that's only for changing the classic textures, to use more textures you have to define custom blocks..
https://www.classicube.net/forum/viewpost/6048-custom_block_creation_a_user39s_field_guide/
The texture has to be served from somewhere, but the web client (rather the browser) is picky. The site must have "access-control-allow-origin: *" from the server. For example dropbox and "raw.githubusercontent.com" (just the raw site not the main ones) do, many others do not. Lemehost's preconfigured VPS does NOT include a web server.
Also for all of them the URL is limited to 64 characters eg: https://raw.githubusercontent.com/rdebath/mc/zip/b...