When attempting to add an account through Workspace App and see this error: 

"Your account cannot be added using this server address. Make sure you entered it correctly. You may need to enter your email address instead."

Using the Storefront URL allows the account to be added

Using the Load Balancing Netscaler URL fails 

• Classic policy expression, in the Expression field, add the following information:  REQ.HTTP.HEADER User-Agent CONTAINS CitrixReceiver
• Advanced policy expression, in the Expression field, add the following information:  HTTP.REQ.HEADER("User-Agent").CONTAINS("CitrixReceiver")

Problem Cause

Netscaler Session policy configuration was set to prohibit this.

REQ.HTTP.HEADER User-Agent NOTCONTAINS CitrixReceiver