The reason why Fulfillment Order does not appear as an option when creating a rollup field on the Order Summary object is that the Order Summary field on the Fulfillment Order object is a Lookup. A Lookup field is a type of custom field that creates a relationship between two objects, but does not support rollup summary fields. To create a rollup summary field, the relationship between the objects must be master-detail, which means that the child record cannot exist without its parent record. Verified Reference: https://help.salesforce.com/s/articleView?id=sf.custom_field_types.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.fields_about_roll_up_summary_fields.htm&type=5

Debugging a flow with input data allows the administrator to test the flow with specific values and see how the flow behaves. The Debug with inputs option is available in the Flow Builder toolbar and lets the administrator provide input values for each flow variable before running the flow. Verified Reference: https://help.salesforce.com/s/articleView?id=sf.flow_builder_debug.htm&type=5

The main types of building blocks when working in Flow Builder are:
Elements: These are the components that define the logic and functionality of a flow. Elements include actions, assignments, decisions, loops, screens, subflows, and waits.
Resources: These are the variables, constants, formulas, collections, and record choice sets that store data in a flow. Resources can be used as inputs or outputs for elements.
Connectors: These are the arrows that connect elements and resources in a flow. Connectors determine the sequence and direction of the flow execution. Reference: [Flow Building Blocks]

The best way for the administrator to meet this requirement is to modify the compact layout on the Credit Memo object. A Credit Memo is a record that represents a refund or credit issued to a customer for an order or part of an order. A Credit Memo has various fields and related lists that display information such as the credit amount, status, reason, etc. A compact layout is a type of layout that determines which fields appear in the highlights panel at the top of a record page in Lightning Experience or Salesforce mobile app. The administrator can use the Object Manager to modify the compact layout on the Credit Memo object and add the Total Amount field to the compact layout. This way, the sales team can see the Total Amount field in the highlights panel at the top of the Credit Memo record page. Verified References: https://help.salesforce.com/s
/articleView?id=sf.order_management_credit_memo.htm&type=5 https://help.salesforce.com/s/articleView?
id=sf.compact_layouts_overview.htm&type=5