diff --git a/app/views/admin/products_v3/_table.html.haml b/app/views/admin/products_v3/_table.html.haml
index 9ffbc22f30..cf581109fd 100644
--- a/app/views/admin/products_v3/_table.html.haml
+++ b/app/views/admin/products_v3/_table.html.haml
@@ -46,7 +46,8 @@
         %th.align-right= t('admin.products_page.columns.actions')
     - products.each_with_index do |product, product_index|
       = form.fields_for("products", product, index: product_index) do |product_form|
-        %tbody.relaxed{ 'data-record-id': product_form.object.id, 'data-controller': "nested-form" }
+        %tbody.relaxed{ data: { 'record-id': product_form.object.id, controller: "nested-form",
+                                action: 'nested-form:add->bulk-form#registerElements' } }
           %tr
             = render partial: 'product_row', locals: { product:, f: product_form }
 
diff --git a/app/webpacker/controllers/bulk_form_controller.js b/app/webpacker/controllers/bulk_form_controller.js
index 189aa9ca05..98a6063a0e 100644
--- a/app/webpacker/controllers/bulk_form_controller.js
+++ b/app/webpacker/controllers/bulk_form_controller.js
@@ -24,6 +24,15 @@ export default class BulkFormController extends Controller {
     window.removeEventListener("beforeunload", this.preventLeavingBulkForm);
   }
 
+  // Register any new elements (may be called by another controller after dynamically adding fields)
+  registerElements() {
+    const registeredElements = Object.values(this.recordElements).flat();
+    // Select only elements that haven't been registered yet
+    const newElements = Array.from(this.form.elements).filter(n => !registeredElements.includes(n));
+
+    this.#registerElements(newElements);
+  }
+
   toggleChanged(e) {
     const element = e.target;
     element.classList.toggle("changed", this.#isChanged(element));
diff --git a/package.json b/package.json
index 771823a69e..f5bd1b0f56 100644
--- a/package.json
+++ b/package.json
@@ -34,7 +34,7 @@
     "shortcut-buttons-flatpickr": "^0.4.0",
     "stimulus": "^3.2.2",
     "stimulus-flatpickr": "^1.4.0",
-    "stimulus-rails-nested-form": "https://github.com/dacook/stimulus-rails-nested-form.git#dist",
+    "stimulus-rails-nested-form": "https://github.com/openfoodfoundation/stimulus-rails-nested-form.git#dist",
     "stimulus_reflex": "3.5.0-rc3",
     "tom-select": "^2.3.1",
     "trix": "^2.0.10",
diff --git a/spec/javascripts/stimulus/bulk_form_controller_test.js b/spec/javascripts/stimulus/bulk_form_controller_test.js
index b0a3386ce9..7571191708 100644
--- a/spec/javascripts/stimulus/bulk_form_controller_test.js
+++ b/spec/javascripts/stimulus/bulk_form_controller_test.js
@@ -181,6 +181,48 @@ describe("BulkFormController", () => {
     });
   });
 
+  describe("Adding new fields", () => {
+    beforeEach(() => {
+      document.body.innerHTML = `
+        <form id="form" data-controller="bulk-form" data-action="custom-event->bulk-form#registerElements",
+          <div data-record-id="1">
+            <input id="input1a" type="text" value="initial1a">
+            <template id="template">
+              <input id="input1b" type="text" value="initial1b">
+            </template>
+          </div>
+          <div data-record-id="2">
+            <input id="input2" type="text" value="initial2">
+          </div>
+          <input type="submit">
+        </form>
+      `;
+    });
+
+    describe("registerElements", () => {
+      beforeEach(() => {
+        // Add new field after controller has initialised
+        input1a.insertAdjacentHTML("afterend", template.innerHTML);
+
+        // Trigger bulk-form#registerElements
+        form.dispatchEvent(new Event("custom-event"));
+      });
+
+      it("onInput", () => {
+        input1b.value = 'updated1b';
+        input1b.dispatchEvent(new Event("input"));
+        // Expect only updated field to show changed
+        expect(input1b.classList).toContain('changed');
+        expect(input2.classList).not.toContain('changed');
+
+        // Change back to original value
+        input1b.value = 'initial1b';
+        input1b.dispatchEvent(new Event("input"));
+        expect(input1b.classList).not.toContain('changed');
+      });
+    })
+  });
+
   // unable to test disconnect at this stage
   // describe("disconnect()", () => {
   //   it("resets other elements", () => {
diff --git a/spec/system/admin/products_v3/products_spec.rb b/spec/system/admin/products_v3/products_spec.rb
index c170187e3a..cb2d746343 100644
--- a/spec/system/admin/products_v3/products_spec.rb
+++ b/spec/system/admin/products_v3/products_spec.rb
@@ -357,7 +357,6 @@ describe 'As an admin, I can manage products', feature: :admin_style_v3 do
         fill_in "On Hand", with: "3"
 
         expect {
-          pending "changes are not detected"
           click_button "Save changes"
 
           expect(page).to have_content "Changes saved"
@@ -432,7 +431,6 @@ describe 'As an admin, I can manage products', feature: :admin_style_v3 do
 
         it "saves changes after fixing errors" do
           expect {
-            pending "changes are not detected"
             click_button "Save changes"
 
             variant_a1.reload
@@ -459,6 +457,125 @@ describe 'As an admin, I can manage products', feature: :admin_style_v3 do
         end
       end
     end
+
+    describe "adding variants" do
+      it "creates a new variant" do
+        click_on "New variant"
+
+        # find empty row for Apples
+        new_variant_row = find_field("Name", placeholder: "Apples", with: "").ancestor("tr")
+        expect(new_variant_row).to be_present
+
+        within new_variant_row do
+          fill_in "Name", with: "Large box"
+          fill_in "SKU", with: "APL-02"
+          fill_in "Unit", with: 1000
+          fill_in "Price", with: 10.25
+          click_on "On Hand" # activate popout
+        end
+        fill_in "On Hand", with: "3"
+
+        expect {
+          click_button "Save changes"
+
+          expect(page).to have_content "Changes saved"
+          product_a.reload
+        }.to change { product_a.variants.count }.by(1)
+
+        new_variant = product_a.variants.last
+        expect(new_variant.display_name).to eq "Large box"
+        expect(new_variant.sku).to eq "APL-02"
+        expect(new_variant.price).to eq 10.25
+        expect(new_variant.unit_value).to eq 1000
+        expect(new_variant.on_hand).to eq 3
+
+        within row_containing_name("Large box") do
+          expect(page).to have_field "Name", with: "Large box"
+          expect(page).to have_field "SKU", with: "APL-02"
+          expect(page).to have_field "Price", with: "10.25"
+          expect(page).to have_content "1kg"
+          expect(page).to have_css "button[aria-label='On Hand']", text: "3"
+        end
+      end
+
+      context "with invalid data" do
+        before do
+          click_on "New variant"
+
+          # find empty row for Apples
+          new_variant_row = find_field("Name", placeholder: "Apples", with: "").ancestor("tr")
+          expect(new_variant_row).to be_present
+
+          within new_variant_row do
+            fill_in "Name", with: "N" * 256 # too long
+            fill_in "SKU", with: "n" * 256
+            fill_in "Unit", with: "" # can't be blank
+            fill_in "Price", with: "10.25" # valid
+          end
+        end
+
+        it "shows errors for both existing and new variant fields" do
+          # Update existing variant with invalid data too
+          within row_containing_name("Medium box") do
+            fill_in "Name", with: "M" * 256
+            fill_in "SKU", with: "m" * 256
+            fill_in "Price", with: "10.25"
+          end
+
+          expect {
+            click_button "Save changes"
+
+            expect(page).to have_content "1 product could not be saved"
+            expect(page).to have_content "Please review the errors and try again"
+            variant_a1.reload
+          }.to_not change { variant_a1.display_name }
+
+          # New variant
+          within row_containing_name("N" * 256) do
+            expect(page).to have_field "Name", with: "N" * 256
+            expect(page).to have_field "SKU", with: "n" * 256
+            expect(page).to have_content "is too long"
+            expect(page).to have_field "Unit", with: ""
+            expect(page).to have_content "can't be blank"
+            expect(page).to have_field "Price", with: "10.25" # other updated value is retained
+          end
+
+          # Existing variant
+          within row_containing_name("M" * 256) do
+            expect(page).to have_field "Name", with: "M" * 256
+            expect(page).to have_field "SKU", with: "m" * 256
+            expect(page).to have_content "is too long"
+          end
+        end
+
+        it "saves changes after fixing errors" do
+          expect {
+            click_button "Save changes"
+
+            variant_a1.reload
+          }.to_not change { variant_a1.display_name }
+
+          within row_containing_name("N" * 256) do
+            fill_in "Name", with: "Nice box"
+            fill_in "SKU", with: "APL-02"
+            fill_in "Unit", with: "200"
+          end
+
+          expect {
+            click_button "Save changes"
+
+            expect(page).to have_content "Changes saved"
+            product_a.reload
+          }.to change { product_a.variants.count }.by(1)
+
+          new_variant = product_a.variants.last
+          expect(new_variant.display_name).to eq "Nice box"
+          expect(new_variant.sku).to eq "APL-02"
+          expect(new_variant.price).to eq 10.25
+          expect(new_variant.unit_value).to eq 200
+        end
+      end
+    end
   end
 
   describe "edit image" do
diff --git a/yarn.lock b/yarn.lock
index 7f7d05d9f5..433742f9b6 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -8350,9 +8350,9 @@ stimulus-flatpickr@^1.4.0:
   resolved "https://registry.yarnpkg.com/stimulus-flatpickr/-/stimulus-flatpickr-1.4.0.tgz#a41071a3e69cfc50b7eaaacf356fc0ab1ab0543c"
   integrity sha512-rcC/c9+E+f5W2kOjaaLShtf3i+p95ACqt+oGzSAgeuZh2YeIN8gW4EWO7h0STBLzSVPl6BjIfPWP7upMPavIVQ==
 
-"stimulus-rails-nested-form@https://github.com/dacook/stimulus-rails-nested-form.git#dist":
+"stimulus-rails-nested-form@https://github.com/openfoodfoundation/stimulus-rails-nested-form.git#dist":
   version "4.1.0"
-  resolved "https://github.com/dacook/stimulus-rails-nested-form.git#d3b82ea638a7156f1122736cf739ab1821a1817e"
+  resolved "https://github.com/openfoodfoundation/stimulus-rails-nested-form.git#d3b82ea638a7156f1122736cf739ab1821a1817e"
 
 stimulus@^3.2.2:
   version "3.2.2"