I have set a scheduled email for a specific date, tried to execute but I get an error, what am I missing?

I have set a scheduled email for a specific date, tried to execute but I get an error, what am I missing?

The error message is

Execution Failed
Error details:
Error in executing form schedule(Form Schedule).
Error.
Error in executing Send Mail task. To Address is NULL.
The function is below

SendMail  
[ 
  From    : zoho.adminuserid
 
  To      : input.email
 
  Subject : "Subscription update"
 
  Message : "Hi " + input.First_name + "<br />\n<br />\nJust a quick not to say your subscription is coming to an end and wanted to check that you still need access to the proxy server<br />\n<br />\nRegards<br />\nStephen<br type=\"_moz\" />"
 

I am wondering if I need to set up email details in zoho for it to work, if so how?

Stephen
]