Extremely frustrating message with no solution

This chat contains some attachments that are not available on this device. To continue this chat, please remove those attachments first. This happens because you started this chat from another device with the attachments and chose not to sync those attachments to the cloud. Note that if you continue the chat on this device, those attachments will be removed from the other devices too.

Which attachment? how do I find it? how do I remove it? why don't you just do it for me? why can't you sync it in the first place? and if you don't sync it that's fine just don't send the attachment