I'm sorry that you're having difficulty with posting to Facebook. I see that you contacted our Support Team and we have a case with our 2nd level of support who will reach out once this is resolved for you.
Apologies for any inconvenience.
All my posts from Constant contact to facebook are gone. i've deleted the FB account. When i go to re add it, i get an Http error 400 (broken link). I was running a sale and event, and now it's not there
I am very sorry to hear that you are experiencing this issue today. Unfortunately, this is an issue that our product support teams are aware of and are working very hard to get fixed as soon as possible. In the mean time you can post manually to your facebook pages using the short URL that is provided for every e-mail that you send. Here are some screen shots that will show you how to get this URL.
Click on actions.
Click on short URL.
Copy the short URL and paste into Facebook.
You will not have the same customization as you do using social share however it will get your e-mail posted to social media quickly until we get this resolved on our end.
I apologize for any inconvenience this may have caused you and hope this helps.
I am sorry that you are running into an error posting to Facebook, it is a known error that we are working on getting fixed. We have taken all the steps that were needed on our end to get this resolved. We are now waiting to hear back from Facebook when everything should be back up.
In the meantime, Ali posted a great workaround for the issue. You can also keep an eye on our Constant Contact Status page to know when Social Share should be working normally.