Referenced variable in a workflow step contains data, but returns an empty value when used

What are you trying to achieve?

I want to connect Voiceflow to a Slack channel. The workflow is triggered when a specific channel receives a new message. That message is used as an input for Voiceflow. I make two HTTP ‘make a request’ steps to first launch Voiceflow and then retrieve a response to the users question. The output is shown in screenshot one. For some reason, when I use the ‘output’ variable as an input into creating a slack message in screenshot two, it returns an error saying there is no data as shown in screenshot three. Any troubleshooting suggestions or advice would be really helpful. Thanks

Steps taken so far

I have tried isolating the issue by assessing whether the variable returns a value with another program, which it doesn’t. I have also tried using a different variable not generated by the HTTP steps as an input, which works. It seems like the issue is with the HTTP steps.

Screenshots: scenario setup, module configuration, errors