comprehend.detectEntities(...).then is not a function

Question

I'm trying to extract the named entities from a given text using AWS comprehend using AWS lambda.

const s3 = new AWS.S3();
const comprehend = new AWS.Comprehend();

function prcObj(text) {
     let res = [];
     return comprehend.detectEntities({
          LanguageCode: 'en',
          Text: text
          }).promise()
          .then( async data => {
               for(let i = 0; i < data.Entities.length; i++) {
                    let phrase = await data.Entities[i].Text;
                    res.push(phrase);
               }
               return res
          })
          .catch(err => {
               return err;
          });
            
}

If I use promise I'm getting promise as result. If I remove promise then I'am getting

2022-11-19T21:24:23.691Z    efcf1adc-5be0-4e20-94e8-dbcf88a8bb55    ERROR   Invoke Error    {
    "errorType": "TypeError",
    "errorMessage": "comprehend.detectEntities(...).then is not a function",
    "stack": [
        "TypeError: comprehend.detectEntities(...).then is not a function",
        "    at prcObj (/var/task/index.js:22:12)",
        "    at Runtime.exports.handler (/var/task/index.js:48:21)",
        "    at Runtime.handleOnce (/var/runtime/Runtime.js:66:25)"
    ]
}

What am I doing wrong here?