If you are planning on uploading a script to Gumroad you can use this function in order to contact Gumroad through the script, and receive a response. Note that it uses JSON.parse, which means you need to have json2.js included in your code in order to convert the response into an object. You can learn more about it here: https://help.gumroad.co…

checkGumroadLicense.jsx

function GumrdLicenseRequest(licenseKeyInput, incrementUseCount, showDialogs) {

    // better check here if there is access to files and network
  
    var showDialogs = (showDialogs == undefined) ? true :  showDialogs;
      licenseKeyInput == undefined ? undefined : licenseKeyInput;
      incrementUseCount == undefined ? false : String(incrementUseCount);
  
  
    if (
      permalink == undefined ||
      licenseKeyInput == undefined ||
      incrementUseCount == undefined
    ) {
      // information is missing, you could print or alert an error 
      return false;
    }

    // make first contact

    var gumroadResponse = "";
    try {
      gumroadResponse =
        String(
          system.callSystem(
            'curl https://api.gumroad.com/v2/licenses/verify -d "product_permalink=' +
            permalink +
            '" -d "license_key=' +
            licenseKeyInput +
            '" -d "increment_uses_count="' +
            incrementUseCount +
            " -X POST"
          )
        ) || "";
    } catch (e) {
      gumroadResponse = "";
      // something went wrong, you could print or alert the error
    }
  

    // finalize the gumroad response as a string
    gumroadResponse =
      String(gumroadResponse).slice(
        gumroadResponse.indexOf("{"),
        gumroadResponse.length
      ) || "";

    // if can establish connection with gumroad, convert the response into an object
    var gumroadRespnseObject = null;
    try {
      gumroadRespnseObject = JSON.parse(gumroadResponse) || "";
    } catch (e) {
      // something went wrong parsing the response, you can print or alert the error
      gumroadRespnseObject = null;
    }
  

    if (gumroadRespnseObject && gumroadRespnseObject.success !== undefined) {
        // gumroad reached succesfully, return the response as an object
      return gumroadRespnseObject;
    } else {
        // did not seem to reach gumroad, probably because no connection to the network has been established
      
      if (showDialogs) {
      alert("Can't reach Gumroad. Are you connected to the internet?");
      }
      return false
    }

    // if made it here contacting gumroad failed for another reson.
    if (showDialogs) {
    alert("Could not contact Gumroad");
    }
    return false;
  };

Thanks for this!
Just a heads up that "permalink" isn't defined or passed into this function so the function currently returns false unless "permalink" is added :)