I am trying to integrate my module in sandbox environment to add data via API

I am trying to integrate my module in sandbox environment to add data via API

I went through the documents and tried to setup the API for adding the module via the api but the problem is the token setup is done on "https://accounts.zoho.in/oauth/v2/token" domain and the bulk write is done on "https://content.zohoapis.com/crm/v8/upload" .

So i am able to generate the token but when i using this token for bulk write i am getting below error.
{
    "ERROR_MESSAGE": "INVALID_OAUTHTOKEN",
    "ERROR_CODE": 401
}

Can someone please help me with the steps that i can do to setup my api to write into my module "Diagnostics".