Hi tharun456, 
Just to make sure, are you referring to the cloudshell-sandbox-plugin or the ssh-credentials-plugin?

Please provide more information about the plugin version you are using.

Thanks!

Recently i have updated jenkins [Jenkins 2.303.3] to this version
Plugins are updated to
credentials-2.6.1
credentials binding -1.27.1
ssh agent-1.24.1
[SSH Build Agents plugin]- [1.806.v2253cedd3295]
[SSH Credentials Plugin]- [277.v95c2fec1c047]
[SSH plugin]-2.6.1

After updating the plugins i am unable to add the ssh server credentials.
In Manage jenkins.

tharun456 you are upgrading to an older version of Jenkins that is not actively supported by the Jenkins community. If the previous version that you were using was before 2.277.1, then you should read the information at https://community.jenkins.io/t/migrating-jenkins/894/5 and should review the upgrade guides for all the versions that are between the base version and the final version of your upgrade. If the previous version was after 2.277.1, then something else may be the issue.

Others will find it very difficult to help you because you have not provided enough information. Others cannot duplicate the issue that you are reporting without that information. Please follow the instructions at "How to report an issue" so that you provide enough information that others may choose to help you.