I have string value in a variable (XYZ), passing this variable in the UiPath.web.activities.httpclient body as shown below, and body format is application/JSON

here is the post request method
public async Task test([FromBody] string teststringdata)
{
try
{
using DBContext context = new();
_ = await context.Database.ExecuteSqlRawAsync("EXEC [xyzStoredProcedure] @teststringdata", new SqlParameter[]
{
new("@testNotes", teststringdata)
});
return Ok();
}
I’m getting 400 error message: “errors”:{“$”:[“‘N’ is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0.”
Example string I’m passing from UiPath in variable XYZ: “NT:Test sending string to post method”
It basically saying the method I have accepts JSON String , not a raw string. So I need help on how I can convert the string value I have defined (XYZ) in UiPath to JSON String