Hello, @gnajith

Would you mind checking the permissions of the WordPress directory? Wordpress will prompt you for FTP credentials if it does not have permission to write the files it needs to.

I believe a similar issue was reported previously in our community:

https://www.digitalocean.com/community/questions/why-i-can-t-install-a-new-plugin-on-my-wordpress

You can check the initial answer from @ryanpq :

If you log in via putty and run the following command (assuming this is an Ubuntu droplet) it will set the files to be owned by the user that the web service is run as and should resolve the problem.

chown -Rf www-data.www-data /var/www/html/

I will recommend you to first check if the WordPress directory is owned by another user and if so to change it in the chown command as well.

Hope that helps!

Let me know how it goes.

Regards,
Alex