diff --git a/api/app/controllers/spree/api/shipments_controller.rb b/api/app/controllers/spree/api/shipments_controller.rb
index e08dbab02a9..c715e3d0fc1 100644
--- a/api/app/controllers/spree/api/shipments_controller.rb
+++ b/api/app/controllers/spree/api/shipments_controller.rb
@@ -95,11 +95,11 @@ def transfer_to_shipment
       private
 
       def load_transfer_params
-        @original_shipment         = Spree::Shipment.where(number: params[:original_shipment_number]).first
+        @original_shipment         = Spree::Shipment.find_by!(number: params[:original_shipment_number])
         @order                     = @original_shipment.order
         @variant                   = Spree::Variant.find(params[:variant_id])
         @quantity                  = params[:quantity].to_i
-        authorize! :read, @original_shipment
+        authorize! [:update, :destroy], @original_shipment
         authorize! :create, Shipment
       end
 
diff --git a/api/spec/requests/spree/api/shipments_controller_spec.rb b/api/spec/requests/spree/api/shipments_controller_spec.rb
new file mode 100644
index 00000000000..203710c29fe
--- /dev/null
+++ b/api/spec/requests/spree/api/shipments_controller_spec.rb
@@ -0,0 +1,136 @@
+require 'spec_helper'
+
+RSpec.describe Spree::Api::ShipmentsController, type: :request do
+  let(:user) { create(:admin_user, spree_api_key: 'abc123') }
+  let(:stock_item) { create(:stock_item, backorderable: false) }
+  let(:variant) { stock_item.variant }
+
+  let(:order) do
+    create(
+      :completed_order_with_totals,
+      user: user,
+      line_items_attributes: [
+        {
+          variant: variant
+        }
+      ]
+    )
+  end
+
+  let(:shipment) { order.shipments.first }
+
+  describe "POST /api/shipments/transfer_to_location" do
+    let(:stock_location) { create(:stock_location) }
+    let(:source_shipment) { order.shipments.first }
+    let(:parsed_response) { JSON.parse(response.body) }
+    let(:stock_location_id) { stock_location.id }
+
+    subject do
+      post "/api/shipments/transfer_to_location.json",
+        params: {
+          original_shipment_number: source_shipment.number,
+          stock_location_id: stock_location_id,
+          quantity: 1,
+          variant_id: variant.id,
+          token: user.spree_api_key
+        }
+    end
+
+    context "for a successful transfer" do
+      before do
+        stock_location.restock(variant, 1)
+      end
+
+      it "returns the correct message" do
+        subject
+        expect(response).to be_success
+        expect(parsed_response["success"]).to be true
+        expect(parsed_response["message"]).to eq("Variants successfully transferred")
+      end
+    end
+
+    context "if the source shipment can not be found" do
+      let(:stock_location_id) { 9999 }
+
+      it "returns a 404" do
+        subject
+        expect(response).to be_not_found
+        expect(parsed_response["error"]).to eq("The resource you were looking for could not be found.")
+      end
+    end
+
+    context "if the user can not update shipments" do
+      let(:user) { create(:user, spree_api_key: 'abc123') }
+
+      custom_authorization! do |_|
+        can :read, Spree::Shipment
+        cannot :update, Spree::Shipment
+        can :create, Spree::Shipment
+        can :destroy, Spree::Shipment
+      end
+
+      it "is not authorized" do
+        subject
+        expect(response).to be_unauthorized
+      end
+    end
+
+    context "if the user can not destroy shipments" do
+      let(:user) { create(:user, spree_api_key: 'abc123') }
+
+      custom_authorization! do |_|
+        can :read, Spree::Shipment
+        can :update, Spree::Shipment
+        cannot :destroy, Spree::Shipment
+        can :create, Spree::Shipment
+      end
+
+      it "is not authorized" do
+        subject
+        expect(response).to be_unauthorized
+      end
+    end
+  end
+
+  describe "POST /api/shipments/transfer_to_shipment" do
+    let(:stock_location) { create(:stock_location) }
+    let(:source_shipment) { order.shipments.first }
+    let(:target_shipment) { order.shipments.create(stock_location: stock_location) }
+    let(:parsed_response) { JSON.parse(response.body) }
+    let(:source_shipment_number) { source_shipment.number }
+
+    subject do
+      post "/api/shipments/transfer_to_shipment.json",
+        params: {
+          original_shipment_number: source_shipment_number,
+          target_shipment_number: target_shipment.number,
+          quantity: 1,
+          variant_id: variant.id,
+          token: user.spree_api_key
+        }
+    end
+
+    context "for a successful transfer" do
+      before do
+        stock_location.restock(variant, 1)
+      end
+
+      it "returns the correct message" do
+        subject
+        expect(response).to be_success
+        expect(parsed_response["success"]).to be true
+        expect(parsed_response["message"]).to eq("Variants successfully transferred")
+      end
+    end
+
+    context "if the source shipment can not be found" do
+      let(:source_shipment_number) { 9999 }
+
+      it "returns a 404" do
+        subject
+        expect(response).to be_not_found
+        expect(parsed_response["error"]).to eq("The resource you were looking for could not be found.")
+      end
+    end
+  end
+end
diff --git a/core/lib/spree/testing_support/authorization_helpers.rb b/core/lib/spree/testing_support/authorization_helpers.rb
index 2ad3e5bd6d3..8400b130093 100644
--- a/core/lib/spree/testing_support/authorization_helpers.rb
+++ b/core/lib/spree/testing_support/authorization_helpers.rb
@@ -60,4 +60,5 @@ def custom_authorization!(&block)
 RSpec.configure do |config|
   config.extend Spree::TestingSupport::AuthorizationHelpers::Controller, type: :controller
   config.extend Spree::TestingSupport::AuthorizationHelpers::Request, type: :feature
+  config.extend Spree::TestingSupport::AuthorizationHelpers::Request, type: :request
 end