I can log in to Poser just fine. The site is a different matter. I don't know if this will help anyone, but I was getting one of those 403 messages when I tried to log in with my PC (Chrome browser and Malwarebytes VPN).  But I noticed I could access the site OK with my ipad.

So, I uninstalled BOTH malwarebyes and Chrome, getting rid of all the stuff in the browser cache. After that I reinstalled BOTH Chrome and Malwarebytes, and now I can access the site without getting the 403 error message.

Problem STILL exists with the amount of time it takes to log in.  It hangs horribly. But at least there is no more 403 error.