Fills in their support line, hours and site - then add this client's account number and PIN.
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Template changes can be pushed to every vendor based on it, from Admin › Vendor Templates.

Vendor ID

Where they post outages, and where you sign in to open a case - link the login itself from the vendor's Logins tab.
What support asks for to check it's you - shown beside the support line, with the PIN hidden until you click it.
Shown on the vendor's page and its quick look.