Explanation
The number of Fulfillment Orders that would be created for this order is one per destination, totaling 3. A Fulfillment Order is a record that represents a group of products in an order that are fulfilled together from the same location. A Fulfillment Order has a lookup relationship to the Order Summary object, and it contains information such as the fulfillment location, delivery method, status, etc. The number of Fulfillment Orders created depends on three factors: Fulfillment Location, Delivery Method and Recipient Address. These factors determine how the Order Items are grouped and allocated to Fulfillment Orders based on routing rules and inventory availability. In this case, since the products must be shipped to three different locations, three Fulfillment Orders are created for each destination. Verified References:https://help.salesforce.com/s/articleView?id=sf.order_management_fulfillment_order.htm&type=5

Explanation
Order Allocation should work on Order Items in Awaiting Allocation status. This status indicates that the Order Item has been confirmed by the customer and is ready to be allocated to a Fulfillment Order based on routing rules and inventory availability. Verified References:https://help.salesforce.com/s/articleView?id=sf.order_management_order_item_status.htm&type=5

Explanation
The number of Fulfillment Orders created depends on three factors: Fulfillment Location, Delivery Method and Recipient Address. These factors determine how the Order Items are grouped and allocated to Fulfillment Orders based on routing rules and inventory availability. For example, if an order has two items that can be fulfilled from different locations, or have different delivery methods or recipient addresses, then two Fulfillment Orders are created for that order. Verified References:https://help.salesforce.com/s/articleView?id=sf.om_order_fulfillment.htm&type=5

Explanation
The type of relationship that exists between FulfillmentOrder and Location is Many-to-One Lookup (Location) FulfilledFrom Location Id. A Lookup field is a type of custom field that creates a relationship between two objects, but does not support rollup summary fields. A Many-to-One relationship means that many child records can be related to one parent record, but not vice versa. In this case, a FulfillmentOrder has a Lookup field named FulfilledFrom Location Id that references a Location record. A Location is a record that represents a physical location from which order product items are fulfilled, such as warehouses and retail stores. A Location can have many FulfillmentOrders associated with it, but a FulfillmentOrder can only have one Location. Verified References:
https://help.salesforce.com/s/articleView?id=sf.custom_field_types.htm&type=5https://help.salesforce.com/s/art

Explanation
Three things that the administrator can do to get more details for debugging when encountering an unhandled fault error are:
Create a fault connector. A fault connector is a special type of connector that handles errors that occur in a flow element, such as an assignment, a loop, or an action. A fault connector can route the flow to another element or end the flow with an error message.
Add a Display Text component which includes {! SFIow.FaultMessage}. A Display Text component is a screen component that displays text on a screen element in a flow. The {! SFIow.FaultMessage} is a system variable that contains information about the error that occurred in the flow, such as the element name, error type, and error message.
Create an error connector. An error connector is a special type of connector that handles errors that occur in a screen element, such as invalid user input or required fields being left blank. An error connector can route the flow to another screen element or end the flow with an error message.
Verified References:
https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_connector_fault.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_screen_component_display_text.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_connector_error.htm&type=5