After creating a full/partial sandbox, when i login to the sandbox and try to access my Merchant facility, i receive the below error “ui.services.connection.api.PartnerConnectionException: INVALID_CROSS_REFERENCE_KEY: Master Encryption Key 1 has already been deleted”
To fix the issue you need to open a case with salesforce and requesting them to enable the feature "Enable Encrypted Custom Objects in Full-Copy Sandboxes." They will ask for the production org ID and Admin username to enable this feature.
This feature needs to be enabled on the production org and then once it is enabled, you will need to refresh your Sandbox.