IAM_PERMISSION_DENIED aiplatform.googleapis.com

Question

I am currently building a node.js script to send a predict request to a Vertex AI endpoint and receive response data back from that. I created a service account with the aiplatform/developer role. I made sure that these permissions were project-level. The script works when I authenticate using the gcloud CLI on my local computer. However, this script will be hosted on a cloud server and I need to use the service account JSON key to authenticate. This is my script below:

const aiplatform = require('@google-cloud/aiplatform');
const { PredictionServiceClient } = aiplatform.v1;
const { helpers } = aiplatform;
require('dotenv').config();

const project_id = '*******';
const location = 'us-central1';
const endpoint_id = '***************';

const client = new PredictionServiceClient({apiEndpoint: "us-central1-aiplatform.googleapis.com"});

async function predictor(instanceData) {
    for (const instance of instanceData) {
        await predict([instance]);
    }
}

async function predict(instances) {
    const endpoint = `projects/${project_id}/locations/${location}/endpoints/${endpoint_id}`;
    try {
        const request = {
          endpoint: endpoint,
          instances: instances,
        };
        const [response] = await client.predict(request);
        parseAndPrintResponse(response);
    } catch (e) {
        console.error('Error during prediction:', e);
    }
}

function parseAndPrintResponse(response) {
    response.predictions.forEach((prediction, idx) => {
        console.log(`Results for Instance ${idx + 1}:`);
        const classes = prediction.structValue.fields.classes.listValue.values.map(v => v.stringValue);
        const scores = prediction.structValue.fields.scores.listValue.values.map(v => v.numberValue);

        classes.forEach((classValue, index) => {
            const score = scores[index];
            console.log(`  Value ${classValue}: ${(score * 100).toFixed(2)}% for ${classValue}`);
        });
    });
}

const instances = [
    {
        "req": "get",
        "type": "query",
        "param": "pages-Size",
        "desc": "Optional filter by items that are missing episodes or not.",
        "dtype": "boolean",
        "bool": "false",
        "b1": "",
        "b2": "",
        "b3": "",
        "b4": "",
        "b5": "",
        "b6": "",
        "zero": "0"
    }
];

const formattedInstances = instances.map(instance => helpers.toValue(instance));

predictor(formattedInstances);

The .env file has the route to the JSON key.But when running this script, I still get the IAM_PERMISSION_DENIED error.