When trying to add a SmartObject step that executes a REST API method in your workflow, you may be required to provide properties of a certain object type. You need to serialize multiple objects into a serialized string, then pass that serialized string into the REST API method.
As such, you may have a single SmartObject step that executes the REST API method, and under the properties, you want to use the context browser to reference the results from the serialized methods of other SmartObjects.
However, the Open Configuration Panel is not showing up when trying to reference multiple serialize methods in that single SmartObjects step that executes the REST API method.
The current workflow designer interface does not support chaining of multiple SmartObjects calls within a single SmartObject step. The Configuration Panel can only be opened when you only add one SmartObject call from the context browser.
The workaround is to not place all the SmartObject calls together in a single step. Create separate SmartObject steps for each of the serialize methods you need to call, and map serialized string in the result into variables. You can reference those variables in the SmartObject method that calls your REST API.