The easiest way to set your channels on vacation mode from Zentail is to disable desired channels from each of your warehouses. This will send 0 inventory to your listings and thus avoid new orders. Zentail will update warehouse availability before the next calendar day.
Go to Account Settings and select a warehouse.
Scroll down to the Warehouse Channel Overrides section and toggle to Disable each of your channels that you want to be sending 0 inventory.
Click UPDATE WAREHOUSE.
Repeat for all of your warehouses.