Why is the post to https://api.easyship.com/2023-01/rates onlyl returning one rate

The API reference states:
The Rates API allows you to request a list of shipping quotes for a prospective Shipment. The response will also indicate which Courier is the cheapest, fastest and best value for money, which is a combination of speed, price and reliability.

However I am only getting one rate back, which has:

"cost_rank": 1.0,
"courier_id": "d70f503c-905b-4e28-a015-d27069a09e0c",
"courier_name": "Evri - Parcelshop",
"courier_remarks": "Pickup option available in checkout",
"currency": "GBP",
"ddp_handling_fee": 0.0,
"delivery_time_rank": 1.0,

Why are other ranked rate options not being returned?