When your gmail won't attach files then another option is to clear the cache and browsing data on your phone. The cache and browse data can cause problems with attachments, so you should disable them. Alternatively, you can switch to another email service if this solution doesn't work. If all else fails, you should contact Google support. If none of the solutions above work, you can try switching back to Gmail. Once you do, you'll be able to attach files with ease!
Read Also: How Do I Fix Gmail Attachment Errors?