Thanks for the information @mkumar. I can see the issue now.
The Referral identified by UBRN 000049792437 is ROUTINE Priority, but your are call to A015 is asking for URGENT appointment slots.
This means A015 will return both URGENT and ROUTINE slots (2WW > URGENT > ROUTINE).
The slot selected for booking (25668997) is an URGENT slot. An URGENT slot cannot be booked to a ROUTINE referral request.
When searching for slots using A015 you should provide the priority of the referral request in the appointmentType query parameter to ensure you only receive slots that are appropriate for the referral.
Regards,
Adam.