So one of the questions I am often asked is from folks that would like to automate a process that is task driven but does not necessarily conform to a simple Approve / Reject set of outcomes. In Nintex Workflow for Office 365 there aren't the same task actions as there are on premises. That being said, you will just need to roll up your sleeves, build a new content type and you'll be all set.
Not sure exactly how to go about building that content type and configuring the Assign Task action to create this single outcome effect? Not a problem.
Below are the steps necessary to make your dreams a reality!*
*Please note that you will need appropriate site owner permissions to accomplish these steps and I cannot guarantee ALL of your dreams will come true. At least the ones that involve tasks assigned with Nintex Workflow. 
- Navigate to Site settings in the context menu under the cog / gear.
- Click on the Site content types link.
- Click on Create.
- Go ahead and give your new task content type a friendly name, description and link it to List Content Types / Workflow Task (2013) and then click OK.
- Now click on the existing Task Outcome column.
- Now in the Change Content Type Column screen, click on Remove.
- Click Ok in the warning popup.
- Now click on Add from new site column. Note that you can remove extraneous columns at this point if you so choose or just leave the default columns alone. It's your choice based on the situation.
- Now go ahead and fill out the create the new outcomes site column configuration screen. Note that the critical part of this step is that you must select Task Outcome for the column type so that the Nintex Workflow designer can pick up the task outcome. Feel free to use a unique name so that you can use it in this workflow but not others. Again, this will depend on how you would like to use this new task content type.
- Click on OK to save the new column.
- Now, navigate back to the site/list/library where you would like to build your workflow and open the Nintex Workflow designer. In the Workflow Gallery open an existing workflow or create a new one.
- Once inside of the designer, drag and drop the Assign a Task action to the canvas and open its configuration dialog by double clicking on the icon or clicking on the Configure in the drop down menu.
- Inside of the configuration dialog, scroll down to and click on Use existing predefined content type.
- Click on the Content Type drop down and select the new custom task content type you created earlier, in my example it was Request Data Task.
- Notice how I only see the single outcome we defined earlier, Completed.
- Now click on Save and you should see an Assign a Task action with a single outcome, which I have renamed to reflect its new functionality.
That's it! Now you can feel free to customize the task form and make any adjustments you see fit to make this task do exactly what YOU want it to do. That's the power of Nintex Workflow. Naturally.
