How to troubleshoot HTTP 403 error?
It's simply a permission problem.
You need to check your server and your website for any kind of security plugin or firewall.
This is a common issue among WordPress users who use Wordfence for their security. If you have it on your website, please see the following tutorial on how to fix the problem via the "learning mode":
If this is not the case for you, you need to contact your hosting company and ask them to check for any security plugin or firewall and if possibly anything is blocking the Depicter requests.