what's "server-defined constant" in your meaning?

for (server's) stored credentials you should see an icon next to username input box

Hi Stephen,

I'm not sure I quite follow, but if you click on the padlock next to the username filed you should be presented with any Credential type workflow constants that have been defined and are available to use. Are you not seeing that?

Regards,

Mark

Using the padlock you can choose from stored credentials.

Credential can be stored I web/site/farm context at these locations: 

/_layouts/15/NintexWorkflow/ManageCredentials.aspx?Scope=Web

/_layouts/15/NintexWorkflow/ManageCredentials.aspx?Scope=Site

/_layouts/15/NintexWorkflow/ManageCredentials.aspx?scope=farm&src=/_admin/NintexWorkflow/Management.aspx

Note: Farm credentials are managed in Central admin.

Thanks I now understand. I appreciate you showing me all the scopes. Once I chose credential it gave me the option to use Secure Store as well. It makes sense now.

Sorry I'm new. I marked mine not yours as correct. I owe you.