Usually it's a server thing. They are not replying in the way they should.
@utxo the webmaster 🧑💻 Could it be the issue the file format? When I post a jpeg it just work in both clients but if I poat a heic file it works only in amethyst because it perform a transformation (compress) before sending it to the server. In the test posting to blossom.band could work because the server performs that transformation contrary to Haven. Could it be the reason? @Vitor Pamplona