diff --git a/Helcim/build.sh b/Helcim/build.sh
index 027c906..06f86d4 100755
--- a/Helcim/build.sh
+++ b/Helcim/build.sh
@@ -9,7 +9,7 @@ rm Helcim.zip
 
 cd build
 
-zip -r ../Helcim.v0.0.1.zip Helcim
+zip -r ../Helcim.v0.0.2.zip Helcim
 
 cd ..
 
diff --git a/Helcim/package-lock.json b/Helcim/package-lock.json
index 1c54b54..08a2177 100644
--- a/Helcim/package-lock.json
+++ b/Helcim/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "postalpoint_helcim_plugin",
-  "version": "0.0.1",
+  "version": "0.0.2",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
diff --git a/Helcim/package.json b/Helcim/package.json
index ce7cdcf..8decb64 100644
--- a/Helcim/package.json
+++ b/Helcim/package.json
@@ -1,6 +1,6 @@
 {
     "name": "postalpoint_helcim_plugin",
-    "version": "0.0.1",
+    "version": "0.0.2",
     "main": "plugin.js",
     "author": "PostalPortal LLC",
     "license": "BSD-3-Clause",
diff --git a/Helcim/plugin.js b/Helcim/plugin.js
index 2ad23b4..8efae0d 100644
--- a/Helcim/plugin.js
+++ b/Helcim/plugin.js
@@ -116,6 +116,10 @@ function getCardBrand(cardType) {
     return cardType;
 }
 
+var currentReceiptID = null;
+
+var checkoutCancelled = false;
+
 exports.init = function () {
     global.apis.pos.registerCardProcessor({
         name: "Helcim",
@@ -133,12 +137,15 @@ exports.init = function () {
             //    it is assumed the payment was successful.
             const code = global.apis.settings.get(PLUGINID + ".devicecode", "");
             const receiptID = global.apis.pos.getReceiptID();
+            checkoutCancelled = false;
+            currentReceiptID = receiptID;
             try {
+                var transactionAmount = global.apis.i18n.moneyToFixed(amount / 100.0) * 1.0;
                 // authorize, capture, add a ReceiptPayment to the receipt, and return boolean true.
                 global.apis.pos.addOnscreenPaymentLog("Getting card payment..."); // Add a line to the onscreen card processing status log
                 var purchaseResp = await apiRequest(`devices/${code}/payment/purchase`, {
                     currency: global.apis.i18n.currency().toUpperCase(),
-                    transactionAmount: global.apis.i18n.moneyToFixed(amount / 100.0) * 1.0,
+                    transactionAmount: transactionAmount,
                     invoiceNumber: receiptID
                 }, "POST", "text");
                 if (purchaseResp.length > 0) {
@@ -151,18 +158,28 @@ exports.init = function () {
                 }
 
                 var paymentID = "";
-
+                var purchaseResp;
                 while (paymentID == "") {
+                    if (checkoutCancelled) {
+                        checkoutCancelled = false;
+                        global.apis.pos.addOnscreenPaymentLog("Checkout cancelled. Warning: It's still possible for the payment to succeed on the reader but not be recognized in PostalPoint; cancel it on the reader too.");
+                        return false;
+                    }
                     await global.apis.util.delay(1000); // Wait a second
                     try {
                         var pollResults = await global.apis.util.http.webhook.poll(WEBHOOK_SOURCE);
                         for (var i = 0; i < pollResults.length; i++) {
                             var resultBody = JSON.parse(pollResults[i].body);
                             if (resultBody.type == "cardTransaction") {
-                                paymentID = resultBody.id;
+                                purchaseResp = await apiRequest(`card-transactions/${resultBody.id}`, null, "GET");
                                 global.apis.util.http.webhook.ack(pollResults[i].id);
+                                if (purchaseResp.invoiceNumber == currentReceiptID) {
+                                    console.log("Got transaction ID from Helcim webhook:", paymentID);
+                                    console.log("purchaseResp", purchaseResp);
+                                    paymentID = resultBody.id;
+                                }
                             } else if (resultBody.type == "terminalCancel") {
-                                if (resultBody.data.deviceCode == code && resultBody.data.invoiceNumber == receiptID) {
+                                if (resultBody.data.deviceCode == code && resultBody.data.invoiceNumber == currentReceiptID && resultBody.data.transactionAmount == transactionAmount) {
                                     paymentID = "CANCEL";
                                     global.apis.util.http.webhook.ack(pollResults[i].id);
                                 }
@@ -174,18 +191,17 @@ exports.init = function () {
                 }
 
                 if (paymentID == "CANCEL") {
-                    global.apis.pos.addOnscreenPaymentLog("Helcim payment not completed.");
-                    global.apis.alert("The card payment was canceled.", "Payment canceled");
+                    global.apis.pos.addOnscreenPaymentLog("Helcim payment not completed: cancelled on the card terminal.");
+                    global.apis.alert("The card payment was cancelled on the card terminal.", "Payment cancelled");
+                    currentReceiptID = null;
                     return false;
                 }
 
-                console.log("Got transaction ID from Helcim webhook:", paymentID);
 
-                purchaseResp = await apiRequest(`card-transactions/${paymentID}`, null, "GET");
-                console.log("purchaseResp", purchaseResp);
                 if (typeof purchaseResp?.errors != "undefined" && purchaseResp.errors.length > 0) {
                     global.apis.pos.addOnscreenPaymentLog("Helcim card payment error: " + purchaseResp.errors[0]);
                     global.apis.alert("Could not finish card payment: " + purchaseResp.errors[0], "Card Payment Error");
+                    currentReceiptID = null;
                     return false;
                 }
 
@@ -200,6 +216,7 @@ exports.init = function () {
                                         pstring
                                         )
                                 );
+                        currentReceiptID = null;
                         return true;
                     }
                 } else if (purchaseResp.status == "DECLINED") {
@@ -209,6 +226,7 @@ exports.init = function () {
                     } else {
                         global.apis.alert("The customer's card was declined.", "Card Error");
                     }
+                    currentReceiptID = null;
                     return false;
                 }
 
@@ -220,6 +238,7 @@ exports.init = function () {
                     global.apis.alert("The transaction didn't complete correctly (Helcim card plugin reached an undefined state)", "Card Error");
                 }
 
+                currentReceiptID = null;
                 return false;
             } catch (ex) {
                 global.apis.pos.addOnscreenPaymentLog(`Error: ${ex.message}`);
@@ -235,6 +254,8 @@ exports.init = function () {
         },
         cancelCheckout: async function () {
             // The user requested to cancel the payment.
+            // Stop the webhook wait loop.
+            checkoutCancelled = true;
         },
         finishPayment: async function ( {checkoutResponse}) {
             // Finish a payment that was authorized but not captured because checkout was called with capture = false