"Sorry, this type of video cannot be saved to this device" error when saving through a shared link

Hello, I have videos that I have exported from After Effects as mp4. I right-click the video and copy the Dropbox link. Then I send it to someone as a text, they can view just fine but when they save it, it goes from 0 to 100 then they get an error. "Sorry, this type of video cannot be saved to this device"

I have sent the same Dropbox link to myself in email, open it, can view it but get the same error.  Saving to/from my iCloud account works fine, it's just to small for everyday use.

There are no strange codecs involved to my knowledge. I have even exported 3 sec. versions of the videos and get the same error, so probably not a size issue. I wish there were better diagnostic tools, instead of just 'you can't'. Any help would be appreciated. It is the only reason I use Dropbox.