There are two ways in Linnworks for automatically assigning shipping services to your orders - Rules Engine and Shipping Mapping.
Shipping Mapping is available for most Channel Integrations and can be used to assign a service to an order specifically based on the buyer's choice on the channel when they placed the order.
Channel Integrations send the shipping method the buyer has selected into Linnworks together with the rest of the order data via XML (Open Orders > View order > Properties > Order XML / in the old OO screen: right-click > View > View Order XML):
Please see the Shipping Mapping documentation page for instructions on setting the correct allocation up for your channel integrations.
Whether you wish to assign the services based on any other criteria on your orders, then please see here for initial steps to start setting up Rules Engine rules for assigning shipping services.
NB! If you are using Rules Engine and Shipping Mapping simultaneously, make sure to add specifications to your rules to exclude the orders which should receive services from the Shipping Mapping. Otherwise, Rules Engine rules will overwrite the Shipping Mapping assignment.