The proposal may contain a link or a URL that cannot be sent, causing the error to occur. Can you send it in plain text without any link and see if the issue persists. Feel free to reply to this post if you need further assistance.
Hi Ms. Mary, I face the same issue. there are no links or urls in my proposal. A job I was trying to apply got closed due to this issue. I'm unable to upload any project files (they are in word format) either. Awaiting a quick reply. thank You.