Thanks for reaching out, @Pushkr.
It looks like the account ID is incorrect. Making a request to the GET accounts endpoint will get you a list of the ads account the authenticated user has access to. (We highly recommend you use twurl for debugging purposes.)
twurl -H ads-api.twitter.com "/2/accounts"
{
"request": {
"params": {}
},
"next_cursor": null,
"data": [
{
"name": "API McTestface",
"business_name": null,
"timezone": "America/Los_Angeles",
"timezone_switch_at": "2016-07-21T07:00:00Z",
"id": "18ce54d4x5t",
"created_at": "2016-07-21T22:42:09Z",
"salt": "54cb7b5a34183f77d82dd6d0f4329691",
"updated_at": "2017-09-24T21:49:51Z",
"business_id": null,
"approval_status": "ACCEPTED",
"deleted": false
}
]
}
In this example, I have access to the following ads account: 18ce54d4x5t. (Note: ads account IDs are base-36 values.)
Please let us know if this helps. Thanks!