Creating a REST API with RPGLE

First, let me say I am trying to do something here that I have zilch
experience with from the IBM i perspective. I have done this type of stuff
using C#.Net on Windows but nothing on the IBM i. Yesterday was my first
voyage into IBM Web Administration for i.

That said, I am trying to create a REST API written in RPGLE that will
return JSON data. I have looked at a lot of examples but just can't find
what I am after.

This needs to be modeled after some existing C#.Net REST APIs so the
following requirements are not negotiable.

The request needs to be a POST type.
The body of the POST request needs to have two "fields".
1) Input - An SQL statement that will be used to retrieve the data.
2) Output - The results of the SQL. These results can be anything so the
fields can't be predefined in the RPGLE program's parameters like they are
in all of the examples that I find. There can also be multiple records so
it would end up having an array in the results. I think I need a single
"results" field that is pretty big and I will need to manually build the
JSON for it.

I tried creating a new HTTP server and deploying a service to it. I have
been successful using Scott's customer lookup as a model and I have been
able to do a few different things to experiment. However, I can't figure
out how to handle the POST body for input or the array results in the
output.

One attempt was to create the following:
dcl-pi *n;
sql char(5000);
resultSet char(50000);
end-pi;
The problem was that I got back a value in the resultSet that was really
junked up JSON because it escaped all of the " as \". I considered trying
to make the resultSet value return as plain text instead of JSON (I'm
assuming I can do that somehow) but I decided before I went too far down the
wrong rabbit hole, I would ask for help.

Can someone help point me in a good direction? I don't mind doing a lot of
web digging, I just don't really know what I need to search for to do the
digging.

Thanks.