On May 15, 2020, we migrated to Square Sandbox v2. Square Sandbox v1 is deprecated and will be retired on May 27, 2020.
Merchants using the Square Sandbox have lost access to it. They have to reconnect to the Sandbox to gain access again.
Sample error: This merchant does not have a location with the ID CBASEDkICwKGE3jsPOA7F3t0wTAgAQ.
Sandbox v2 has a new location, the new location will be set after reconnecting the Sandbox
Merchant has to clear subscriptions / customers / revenue to disconnect the payment gateway.