Ayushmann Deb, Thanks for the comment. If you read carefully I have mention that need to replace previously captured successful access token. Paste the section below. I got the token from my send account. only change the mobile number within this token.

Submit the Modified Request: At this point, I change the response code to ‘200 OK’ and use the previously captured successful access token.

for more deatils you can reach out to me on linkedin.