How to implement server to server callback for rapidoreach SDKs?

You can use request method which comes by default with node.js or by using axios library for server to server callback, but a quick check at rapidoreach site (https://www.rapidoreach.com/docs#/callbacks) leads to this doc for callback setup and looks like you want to receive callbacks, in that case you have to setup a api at your end to receive their server call, this is one example done in Nodejs

Example:

        function rapidoreachPostback(req: Request, res: Response) {

      var IP = req.headers['x-forwarded-for'] || req.connection.remoteAddress;
      var Input = req.query;
      
      if (Input.status == 'C' || Input.status == "P" || Input.status == "F") {

        if(Input.status === "C"){
          //record your completion here
        }
    
        //if rapidoreach allows disaqualification points
        if(Input.status === "P"){
          //record your disqualification transaction over here
        }
        if(Input.status === "F"){
          //record your survey offer failure transaction over here
        }
        
        }
          } catch (error) {
            // send "1" in response to server call from rapidoreach.
            res.send("1");
            return;
          }
          res.send("1");
    
          return;
        })
        return;
      }
      res.send("1");
      return;
    }
    
    

Rapidoreach will send server to server callback using get request to the callback URL maintained in App setings.

Assuming Callback URL in app settings is set as

https://local.callback.com/callback.php

Below is an example of server to server callback. Details of parameters available in callback can be found in their official docs https://www.rapidoreach.com/docs#/callbacks

https://local.callback.com/callback.php?cmd=P&userId=SYKUser-CvkBPlfibeV-aba04fe2fc72219fdbb9a9353a68713d&amt=0.01&offerInvitationId=trans0002&status=P&offerHash=4fdcc6461ec225ba8af3bc66ccf4017c&currencyAmt=0.80&transactionId=trans0002&endUserId=SYKUser&txnHash=d5fecc45d5be250ff757f8694a6d65a1&useragent=Rapidoreach&currencyName=Local Coins&offerType=1&deviceType=Desktop&intergrationMethod=IFRAME

Here is an example how you can handle callback using PHP.

File callback.php

<?php

/**
 * ApplicationKey can be found in credentials tab of app created in Rapidoreach
 */
$ApplicationKey = "<Replace this>"; //<- replace this with real application key

/**
 * $endUserId is unique endUserId in publisher's system.
 */
$EndUserId = $_REQUEST['endUserId'];

/**
 * Unique offer Id 
 */
$OfferInvitationId = $_REQUEST['offerInvitationId'];

/**
 * TransactionId
 */
$TransactionId = $_REQUEST['transactionId'];

/**
 * Status
 *    C: Completed - User has successfully completed an offer and should be rewarded with currencyAmt
 *    P: Attempted - User has attempted an offer and attempt is valid will be rewarded with currencyAmt
 *                  currencyAmt will not be full in this case and will be equal to screenout reward maintained in App Setting of Rapidoreach Publisher portal
 *    F: Failed - User has failed to complete an offer and hence terminated. No rewards should be awarded
 */
$Status = $_REQUEST['status'];

/**
 * Validate offerHash
 * You should verify oidHash upon receipt of the callback by recomputing it with the callback offerInvitationId and your ApplicationKey. 
 * This will secure against users faking their own id and passing it in if by some chance they come across the script.
 */
$offerHash = $_REQUEST['offerHash'];
$CalculatedOfferHash = md5($OfferInvitationId . $ApplicationKey);
if ($offerHash != $CalculatedOfferHash) {
  /**
   * TODO: User is trying to manupulate offerId to get credits. Flag this user within this condition if required (optional).
   * Do not credit this user and send success response to Rapidoreach
   * Do not continue further
   */
  echo "1";
  die;
}

/**
 * Validate txnHash
 */

$txnHash = $_REQUEST['txnHash'];
$CalculatedTxnHash = md5($TransactionId . $ApplicationKey);
if ($txnHash != $CalculatedTxnHash) {
  /**
   * TODO: User is trying to manupulate transaction id to get credits. Flag this user within this condition if required (optional).
   * Do not credit this user and send success response to Rapidoreach
   * Do not continue further
   */
  echo "1";
  die;
}

/**
 * Credit the user based on offer status
 */

switch ($Status) {
  case 'C':
    # TODO: Credit the $EndUserId with $currencyAmt use $TransactionId to avoid duplicates
    echo "1";
    die;
    break;
  case 'P':
    # TODO: Credit the $EndUserId with $currencyAmt use $TransactionId to avoid duplicates
    echo "1";
    die;
    break;
  case 'F':
    # TODO: User has failed to complete an offer
    echo "1";
    die;
    break;

  default:
    # code...
    break;
}