Paypal Integration - Unable to create dispute in buyer's UI in sandbox

[land_pol]

Hi, 


We are successfully developing Paypal integration. Hopefully someone can help us with a minor setback.

In late July we started looking into the Disputes use case. 
As a proof-of-concept, we used a buyer sandbox account to create a new dispute case on completed transactions (image below) and were able to receive Paypal's notifications regarding that dispute.

 
Unfortunately we just noticed that the "Report a problem" functionality we've been using in sandbox is now leading to an error page (images below). 

The URL provided in "Report a problem" was the following:
https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_comres_flow&trans_id=67N72280SX984472A&select_dis...

Has anyone come across this issue? Can anyone help us understand what has changed in the past month that is blocking us from using this feature?


Best regards, thanks in advance.

[land_pol]

FYI

The "Report a problem" functionality is now up and running in sandbox.

[land_pol]

Unfortunately, we can't use the seller's UI to respond to all types of disputes. 
For instance, the seller can respond to "Item not received" disputes but not "Unauthorised transaction" ones.