Base on the screenshot, the GetAttachmentsList method is failing because it is expecting an ID input, but did not get one.

Is this SharePoint List item attachments?  If so, usually you need to pass into this method the ‘List Item ID’ as it would be a required field for determining which List Item it should retrieve the attachments from.

• List ID = 1, Title = Test1
  • Attachment1
  • Attachment2
• List ID = 2, Title = Test2
  • Attachment1
  • Attachment2

You can use a Show a message box action before this GetAttachmentsList action to see if the field that you are mapping as the List Item ID has a value or not.

Or if this is on initialize, you can add a condition that says only execute the GetAttachmentsList action if the View Parameter or field that you are passing in contains a value.

As you can see, I added the get attachment list rule and I configured it with the ID parameter I added and still not work. 

Please attach a screenshot of how the input mapping for this action is configured by clicking on the (Configure) option.  There is usually a required List ID field that needs a value for this method to execute successfully.

And if there isn’t an List ID when this list view is used in states, then you will want to add a condition that says only execute this method if that ID field is populated.