This is probably the issue. You cannot have newlines in a JSON string, and the \ character needs to be escaped, so that your \n should look like \\n.
Alternatively, as you want the output in HTML, simply use a HTML line-break tag <br>.
A much simpler solution could be to use my “Collection to Array/String List” module, available here.
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: investing some effort into the tutorials in the Make Academy will save you lots of time and frustration using Make!