Explanation
Two possible reasons that could cause the test org to not appear in the list of target organizations are:
The components in the Change set could not be found within the test org. This means that the test org does not have the same metadata components or features as the development org, and therefore cannot receive the change set.
The development org has not been approved to upload Change Sets from within the test org. This means that there is no deployment connection between the two orgs, and the test org has not authorized the development org to send change sets to it.
Verified References: https://help.salesforce.com/s/articleView?id=sf.changesets_about.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.changesets_create_outbound.htm&type=5

Explanation
Two ways that Order Management licenses can be assigned are:
By Permission Set. A Permission Set is a collection of settings and permissions that give users access to various tools and functions in Salesforce. A Permission Set can be assigned to individual users or groups of users, regardless of their profile or role. An administrator can create a Permission Set that includes the Order Management User permission, which enables users to access Order Management features and data. The administrator can then assign this Permission Set to the users who need Order Management licenses.
By User. A User is a record that represents a person who can log in and access Salesforce. A User has various fields and settings that determine their access and permissions in Salesforce, such as profile, role, license type, etc. An administrator can assign an Order Management license to a user by editing the user record and selecting Order Management User from the License Type picklist. The administrator can also enable the Order Management User permission on the user record.
Verified References:
https://help.salesforce.com/s/articleView?id=sf.order_management_user_permission.htm&type=5https://help.sal

Explanation
Three components that can be used to modify the user experience in the Order Summary detail page are:
Tabs. Tabs are a type of component that allow users to switch between different views or subpages on a record page. Tabs can contain other components, such as charts, reports, or custom components, that display different information orfunctionality related to a record. The administrator can use the Lightning App Builder to add and customize tabs on the Order Summary detail page to give users more options and flexibility.
Accordion. Accordion is a type of component that allow users to expand and collapse sections of a record page. Accordion can contain other components, such as fields, related lists, or custom components, that display different information or functionality related to a record. The administrator can use the Lightning App Builder to add and customize accordion on the Order Summary detail page to give users more control and visibility.
Related List-Single. Related List-Single is a type of component that displays a single related list for a record. A related list is a list of records that are linked to another record by a relationship field, such as lookup or master-detail. The administrator can use the Lightning App Builder to add and customize related list-single on the Order Summary detail page to give users more access and context.
Verified References:
https://help.salesforce.com/s/articleView?id=sf.lightning_app_builder_components.htm&type=5

Two ways that Order Management licenses can be assigned are:
By Permission Set. A Permission Set is a collection of settings and permissions that give users access to various tools and functions in Salesforce. A Permission Set can be assigned to individual users or groups of users, regardless of their profile or role. An administrator can create a Permission Set that includes the Order Management User permission, which enables users to access Order Management features and data. The administrator can then assign this Permission Set to the users who need Order Management licenses.
By User. A User is a record that represents a person who can log in and access Salesforce. A User has various fields and settings that determine their access and permissions in Salesforce, such as profile, role, license type, etc. An administrator can assign an Order Management license to a user by editing the user record and selecting Order Management User from the License Type picklist. The administrator can also enable the Order Management User permission on the user record.
Verified Reference: https://help.salesforce.com/s/articleView?id=sf.order_management_user_permission.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.users_understanding_license_types.htm&type=5

The best practice to create this functionality is to use a Process Builder. A Process Builder is a declarative tool that allows administrators to automate business processes based on certain criteria and actions. The administrator can create a Process Builder that triggers when a Fulfillment Order is created, and then executes an Outbound Message action that sends the information to the external accounting system. Verified Reference: https://help.salesforce.com/s/articleView?id=sf.process_overview.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.process_action_outbound_message.htm&type=5