I tried again and successfully logged into PP Sandbox using a "buyer" login rather than my Sandbox "master" account, so to speak. (Don't know why that didn't work yesterday.) I did get further in that a screen came up asking me to "Review Your Information", which reflected the information I used in setting up this "buyer" account. (Similar to what I see when logging into a normal account.)
However, after clicking the Continue button, I promptly get a "The page cannot be displayed because an internal server error has occurred." error message. I don't know if this is internal to the PayPal Sandbox (I suspect it is) or to PowerStore 2.0. I tried three times but always get the same error message. I may try again later to see if it clears up on its own.
Any thoughts? Thanks.