Hello @HCDDSPmaz , 

Is the External API Cloud based or On-Premise?

If it is On-Premise  you will need to install the Nintex Gateway on a server in your LAN.

To integrate with a custom API you need to create your own custom Xtension. 1st check the Connector Gallery (https://gallery.nintex.com/) to see if it has not been done already.

If not, you will need to get/create a OPEN API c2.0 specification, also called a SWAGGER definition. This Swagger File is used to create a Custom Xtension on your NAC tenant.

Nintex Help is an excellent resource when it comes to explaining how to create your own Xtension:

https://help.nintex.com/en-US/xtensions/Home.htm

For connecting to an external API in NAC, use the “Call a web service” action in the workflow.  You may also have to add a “Query JSON” action to parse the results.  If you want to retrieve the data from that API on a workflow start form, then you may want a custom Xtension.  See the examples on this page -- 

Xtension examples

Or you may also want to build an Xtension to create an available workflow action that returns results in a simpler form.  For example, see the AccuWeather Forecast Xtension example on that page.

Thank you both for your responses. I am going to try what you said and I have any more questions I’ll let you know.