This error happens after the actual posting, so the post is correctly sent and you should not retry.[WebPush] curl extension is not loaded but is required. You can fix this in your php.ini.
Note that if you are a new user, or this is your first post/reply, it will take until a moderator approves it to actually show (should not take more than 1-2 days, feel free to contact me if it isn't). Your next posts won't have this restriction.
So, next time you see the error, just go back to the forum and refresh. It will appear there (although maybe not yet if still pending moderation).