Inconsistent responses from shipment endpoint

[ahmedkhabar]

I'm trying to get shipment details, but I'm getting inconsistent responses; sometimes I get the necessary information, and sometimes I get the following response:

{
 "response": {
 "errors": [
 {
 "code": "TV1002",
 "message": "Invalid inquiry number"
 }
 ]
 }
}

N.B. I'm sure that the inquiry number is correct. also, I check it in the UPS tracker, and I got the details without a problem