not sure how that link renders in your client, but for blossom it has to be https:// not wss://
you have a blossom server already, mate! add https://relay.inpc.cat to the top of your clients blossom server list! :aliendance:
Discussion
Ah ok, I really need to read up on Blossom servers.
There's more to it, but the main difference from, say fediverse upload, is that the file hash becomes the file name. So a client can query the server indicated in the note for the file, but if it is not there, it can look for the same file on any other blossom server it knows of. Typically, the access control is different from the things you are used to. I.e. your haven relay on relay.inpc.cat will not accept files from anyone else than you, and that's why you have to sign an event for the blossom to accept the file.