@jk the .cloud admin probably has kznk.me set to reject all media files.
Given the following:
* It's a Japanese-centric instance.
* Both admins have anime girl avatars.
* The code of conduct is incredibly sparse.
1+1+1 = It's probably because of Japanese drawn child pornography.
[Notice Regarding the Transfer of the mstdn.jp / mastodon.cloud Services] We have received several inquiries showing interest in a transfer following the announcement of the end of the mstdn.jp and mastodon.cloud services. As a result of subsequently evaluating the situation and making preparations, we have decided that the corresponding services will be transferred to a company in the United States on June 30. We will make an announcement regarding the name of the company that the services will be transferred to once preparations have been made. Thank you.