The API is working correctly. In this example, it returns a default response.

To get a real (non-default) response, please execute the following query:
SELECT sm.request_id, sbi.MILESTONE_ID
FROM SRD_MILESTONE sm
INNER JOIN SRD_BOQ_ITEM sbi
ON sm.id = sbi.MILESTONE_ID
WHERE DTYPE = 'FIBER';
This will provide a list of request_id values that can be used for testing and should return non-default data.

Please also refer to the attached screenshot, where I tested this in my local environment.

To be demoed in SRD §UI

1) Find a request with an active FIBER task (status=BOQ_IN_PROGRESS). Run this to confirm:
2) Then Fill Fiber BOQ in the UI
Open request -> Fiber tab -> BOQ section -> add at least one BOQ item then save.
3) Call the API

<srd:getFiberDesignParameters>
<requestId>...</requestId>
<serviceName>empty</serviceName>
</srd:getFiberDesignParameters>

4) Show the customer

UI (Fiber tab) API Response