Can not integrate sandbox.paypal.com with sandbox.authorize.net

[adn_user]

I login to sandbox.authorize.net. I click on Account > Digital Payment Solutions > PayPal. I click Sign Up. I click grant permissions. I see the screen with permissions. I'm logged into my sandbox.paypal.com account.

I click Grant Permissions. I am returned to the Digital Payment Solutions page but I get the message: "There has been an error while processing your request. Please try again"

When I'm looking at the grant permission page, the url is:

https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_grant-permission&request_token=<token>

All help or suggestions for investigation deeply appreciated. 

[adn_user]

Update: when I go into my paypal account > account settings > service providers, I do see Test AuthorizeNet's Test Store with email anet@visa.com.

[adn_user]

I also see that Authorize.net is listed in the pre-build payment solution area of paypal credentials/account access. When I click on manage API permissions, I do see the permissions for anet_api1.visa.com as probably expected.

[adn_user]

I talked to support and they said that the authorize.net sandbox <> paypal sandbox link is known to be broken.

They didn't offer any ETA.