I recreated this Action and am now getting an error: Request body cannot be empty

isn't it a call webservice action an option for you?

it might be easier to make it working.

anyway, from formal point of view content of your request seems to be correct.

so make sure you supply correct data into it. let them write to history log and double check they are correct.

if your variables might contain sensitive characters try to XmlEncode() request content before you supply it to web service.

I can try the Web Service call, but there is less documentation out there than for the Web Request and I'm not 100% sure if I know how to create the dictionaries necessary. I'll see what I can find.

Since the users who are going to be using the list aren't admins, I am thinking that I will also need to use the Web Service call within an App Step?

advantage of web service call action is that it reads service definition and provides you with a field for all the inputs the service needs.

it as well builds request XML, so you need not to spent so much time studying web service. you just need to understand what input data are expected.

I even think that there is not needed any extra documentation for the action itself, I think description in the documentation should be sufficient. as I said, it's moreless about understanding what input data are needed.

I do not know what you mean with "create dictionaries", can you explain that?

yes, you will need to execute AddGroup web service call with sufficient credentials to do that.

First, thank you for the help. In Office 365, the Call Web Service Action does not look like the On-Prem version. That is what I tried first, because I am familiar with the On-Prem version. It works well and like you describe On-Prem. In Office 365 you need to create dictionary variables for Headers and Content. At least you have to in my tenancy. Does yours look different? Please see the screen shots.

ok, I see now.

I do not have experience with 0365 so I haven't realized the difference to on-prem.

however, I think these links might help you with web service and dictionaries (if you haven't seen them already)

Dictionary Part 3 - Call Web Service result into a Dictionary

http://www.vadimtabakman.com/nintex-workflow-dictionary.aspx

an this regarding web request

Web Request action for O365

I did finally get this sorted out. I had an awful time with both the Web Request and Call HTTP Web Service, but the issue was not with those Nintex Workflow actions, it was with configuration of SharePoint Online itself. I needed to enable the feature "Workflows can use app permissions", then set app permissions for the Workflow App Identifier, then run the Web Service call in an App Step.

This link explains what was done​ to fix the issue.

After I did that and set up all the dictionaries, I got the Call HTTP Web Service action to work.