When an order is generated on jet.com, then the merchant should notify jet.com that whether he is able to fulfill the orders or not.
For this purpose:-
Go to Jet > Order > View Details.
The orders will be shown here.
Click Acknowledge button to acknowledge the order.
If Acknowledge button is clicked then that order cannot be rejected.
If Auto-Acknowledged field on Jet>jet Configuration>Extra Settings is set to true then the order fetched will be automatically acknowledged on jet.com as well as on Woocommerce Shop.
This is done so that if the merchant is unable to acknowledge the orders within few hours then they don’t get rejected.