Ok, what am I doing wrong, while trying to publish a NIP-94 event?

Based on python-nostr (https://github.com/jeffthibault/python-nostr) I am passing as described in NIP-94 (https://github.com/nostr-protocol/nips/blob/master/94.md) a specific kind and the needed tags, such as url, m and x. I left optional tags.

As a result I receive a signed event which is published to some relays:

Event(content='nip-94 test', public_key='12459f0dd8980755ca545fc8c2ae3c19391129c9037a045298abb6a6006fb45d', created_at=1683465856, kind='1063', tags=[['url', ''], ['m', 'image/jpg'], ['x', '27661c33adc93a8b3b0dddc7996e0aa48dbe637c879f3ca514a368c75d50953a']], signature='4d22bb8c1e872e91a9572a28d835c59613d864a935a02c9153be58becddafee46da51a3ef746f8046502eb9d4a78ed0423ee5267433735929e9b175e1fd69590')

Querying relays with https://nostr.info/relayr/ shows, that the event should be received, but it is not visible in all my clients. Did I something wrong or did I misunderstand NIP-94?