Cannot confirm shipment and buy Lable

Hello,
I am working on the sandbox environment
I have an error I am facing while trying to confirm a shipment via API.
First I created the shipment via this endpoint: https://api.easyship.com/v2/shipments
Then I tried to confirm shipment and buy label using the endpoint: https://api.easyship.com/label/v1/labels.
I however got the response when I used the easyship_shipping_id gotten :

"message": "Shipments not found or labels already requested: ESUS10077829",
"errors": [
"Shipments not found or labels already requested: ESUS10077829"
],
"labels": [],
"total_cost": null,
"available_balance": -176.22

And when I try to tack the shipment, I still get a valid response. What am I doing wrong please?