Send button on DocuSign is not Working

Hi Nitish,

One of the reason may be that your DSProSFUsername should match to your Docusign API User name
You can view and  edit the DSProSFUsername in Salesforce:

Setup >> Manage Users>> Users >> Selecting the Username >> Edit >> Populate either the DocuSign API Username.If you cannot view, you may have to add "DSProSFUsername" to the Layout.

You can locate the the API Username in Docusign:

Account Preferences >> Member Options >> Permissions >> Under DocuSign API >> API UserName

Another reason for it may be:
Org wide default security settings for the Docusign Account configuration object in SF, were set to Private which was prevents non admin users from accessing these configurations. Setting this to Public Read/Write may solve your issue.

Thanks.