When trying to use the $data attribute in a json string, is it mandatory that one of the available SDKs be utilized in order to access the contents of $data?

In Adaptive Card Designer, I can access and display $data's contents just fine, but when posting to MSTeams, for example, I just see the reference e.g. ${header1} instead of the actual data that I want to display.

I have followed the documentation Option A: Inline data.

I'm mainly doing this via curl POST. Static content(e.g. writing the data directly into the json string) works just fine but I'm pretty sure it's just my understanding on how it should or would work that's lacking.

How should I workaround this issue?