Hello,
First of all, your assertionIssuer should indeed be the same as Client Key.
I think your Token Service URL is not correct... it should look like: https://pmsalesdemo8.successfactors.com/oauth/token
An other note is that I think since a few weeks ago (like I explained in my previous post), these links might not be working anymore (can you try in an external tool such as postman to get some response ?). Since you are not using the same system than me, I am unsure of the new oData link but it might be api8.successfactors.com or apisalesdemo8.successfactors.com.
Cheers
Greg