And here is the portion of the response that I'm trying to match.
I found my problem.
When reading the HTTP response as a JsonObject, I was using GetJsonText to retrieve the response as text. However, this would add backslash characters to properly escape special characters such as double quotes. This caused my regex to not match the portion of text I was looking for. To fix this, I used GetLongchar which returned the text without the added characters.