Hi Khadija,
I've just developed a connector for one client to poll data from MixTelematix API, constantly fetching vehicle locations.
In my case, as there are some rules to check location etc. so I didn't use the out-of-box connector to request the API.
Two suggestion I would give here:
1. Get a valid token for API
In my case, I used code to generate bearer token first and use this token in the header for subsequent requests rather than you using credential details in the header.
I would agree with Stefan using another approach to test your way to communicate with api first. I was using Postman to ensure the parameters provides are correct.
2. Import certificate into GEP
Otherwise, you would get some error in logs like... invalid certificate..PKIX.
You seem didn't arrive at this stage yet.