First of all, make sure your workflow is active on the canvas. If the workflow is active, the problem might be that you are executing it manually and the data, in that case, might not get fetched into the second workflow. From the current information you have provided, it should work when it’s in production.
If you want to test the workflow and need the data, you can copy the data from the first workflow and create a function so you can run your tests.
Check this thread on how to mock the data structure your parent workflow would later pass on in production mode.