and your message will end up to drafts with the attachment. Affected Google services include Gmail, Drive, Docs, Groups, Chat/Hangouts, Meet, Keep and Voice.Message could not be sent. Check your network and try again.
In their status page Poople is writing "Our team is continuing to investigate this issue." so at least they are aware of the issue and admit it instead of trying to cover it up as before. Some past issues with Gmail have taken a very long time to fix if ever so better not hold your breath.
Meanwhile, you can still send attachments using competing email and instant messaging services. If you find another workaround to this issues, please let me know.