fix(taxes): skip zero-amount fees in the Anrok tax payload

app/graphql/mutations/integrations/fetch_draft_invoice_taxes.rb

@@ -50,6 +50,8 @@ def fixed_charge? = false
         def commitment? = false
 
         def subscription? = false
+
+        def taxable? = sub_total_excluding_taxes_amount_cents.positive?
       end
 
       def invoice(customer, args)

app/services/fees/apply_provider_taxes_service.rb

@@ -14,6 +14,7 @@ def initialize(fee:, fee_taxes:)
     def call
       result.applied_taxes = []
       return result if fee.applied_taxes.any?
+      return result if fee_taxes.nil?
 
       applied_taxes_amount_cents = 0
       applied_precise_taxes_amount_cents = 0.to_d

app/services/integrations/aggregator/taxes/invoices/base_service.rb

@@ -18,6 +18,22 @@ def initialize(invoice:, fees: nil)
 
           delegate :customer, to: :invoice, allow_nil: true
 
+          # NOTE: Only fees with a positive amount can incur tax, so non-taxable fees are
+          #       excluded from the provider request. This keeps the payload under the provider
+          #       line-item limit (Anrok and Avalara reject payloads above 1200 items).
+          #       Excluded fees are absent from the response and keep their zero taxes.
+          def taxable_fees
+            @taxable_fees ||= fees.select(&:taxable?)
+          end
+
+          # NOTE: With no taxable fee the request would carry an empty line-item array, which
+          #       both providers reject. There is nothing to tax, so skip the provider and
+          #       report no fee taxes.
+          def no_taxable_fees_result
+            result.fees = []
+            result
+          end
+
           def process_void_response(body)
             invoice_id = body["succeededInvoices"]&.first.try(:[], "id")
 

app/services/integrations/aggregator/taxes/invoices/create_draft_service.rb

@@ -12,6 +12,7 @@ def action_path
           def call
             return result unless integration
             return result unless ::Integrations::BaseIntegration::INTEGRATION_TAX_TYPES.include?(integration.type)
+            return no_taxable_fees_result if taxable_fees.empty?
 
             throttle!(:anrok, :avalara)
 
@@ -44,7 +45,7 @@ def payload
               invoice:,
               customer:,
               integration_customer:,
-              fees:
+              fees: taxable_fees
             ).body
           end
         end

app/services/integrations/aggregator/taxes/invoices/create_service.rb

@@ -12,6 +12,7 @@ def action_path
           def call
             return result unless integration
             return result unless ::Integrations::BaseIntegration::INTEGRATION_TAX_TYPES.include?(integration.type)
+            return no_taxable_fees_result if taxable_fees.empty?
 
             throttle!(:anrok, :avalara)
 
@@ -46,7 +47,7 @@ def payload
               invoice:,
               customer:,
               integration_customer:,
-              fees:
+              fees: taxable_fees
             ).body
 
             invoice_data = payload_body.first

spec/graphql/mutations/integrations/fetch_draft_invoice_taxes_spec.rb

@@ -138,6 +138,86 @@
     expect(breakdown2["enumedTaxCode"]).to eq("reverse_charge")
   end
 
+  context "when a fee has no amount" do
+    let(:fees) do
+      [
+        {
+          addOnId: add_on_first.id,
+          unitAmountCents: 1200,
+          units: 2,
+          description: "desc-123",
+          invoiceDisplayName: "fee-123",
+          fromDatetime: current_time.utc.iso8601(3),
+          toDatetime: current_time.utc.iso8601(3)
+        },
+        {
+          addOnId: add_on_second.id,
+          unitAmountCents: 0,
+          units: 1,
+          description: "desc-12345",
+          invoiceDisplayName: "fee-12345",
+          fromDatetime: current_time.utc.iso8601(3),
+          toDatetime: current_time.utc.iso8601(3)
+        }
+      ]
+    end
+
+    it "excludes it from the request" do
+      execute_graphql(
+        current_user: membership.user,
+        current_organization: organization,
+        permissions: required_permission,
+        query: mutation,
+        variables: {
+          input: {
+            customerId: customer.id,
+            currency:,
+            fees:
+          }
+        }
+      )
+
+      expect(lago_client).to have_received(:post_with_response) do |payload, _headers|
+        expect(payload.first["fees"].map { |fee| fee["item_id"] }).to eq([add_on_first.id])
+      end
+    end
+  end
+
+  context "when no fee has an amount" do
+    let(:fees) do
+      [
+        {
+          addOnId: add_on_first.id,
+          unitAmountCents: 0,
+          units: 2,
+          description: "desc-123",
+          invoiceDisplayName: "fee-123",
+          fromDatetime: current_time.utc.iso8601(3),
+          toDatetime: current_time.utc.iso8601(3)
+        }
+      ]
+    end
+
+    it "returns no tax results without calling the provider" do
+      result = execute_graphql(
+        current_user: membership.user,
+        current_organization: organization,
+        permissions: required_permission,
+        query: mutation,
+        variables: {
+          input: {
+            customerId: customer.id,
+            currency:,
+            fees:
+          }
+        }
+      )
+
+      expect(result["data"]["fetchDraftInvoiceTaxes"]["collection"]).to eq([])
+      expect(lago_client).not_to have_received(:post_with_response)
+    end
+  end
+
   context "when there is tax error" do
     let(:body) do
       path = Rails.root.join("spec/fixtures/integration_aggregator/taxes/invoices/failure_response.json")

spec/services/fees/apply_provider_taxes_service_spec.rb

@@ -94,6 +94,19 @@
       end
     end
 
+    context "when the fee was not reported to the tax provider" do
+      let(:fee_taxes) { nil }
+
+      it "leaves the fee untaxed" do
+        result = apply_service.call
+
+        expect(result).to be_success
+        expect(result.applied_taxes).to be_empty
+        expect(fee.applied_taxes).to be_empty
+        expect(fee).to have_attributes(taxes_amount_cents: 0, taxes_rate: 0)
+      end
+    end
+
     context "when fee already have taxes" do
       before { create(:fee_applied_tax, fee:) }
 

spec/services/integrations/aggregator/taxes/invoices/create_draft_service_spec.rb

@@ -130,6 +130,54 @@
           expect(result.fees.first.tax_breakdown.last.rate).to eq("0.00")
         end
 
+        context "when a fee has no amount" do
+          let(:fee_add_on_two) do
+            create(
+              :fee,
+              invoice:,
+              add_on: add_on_two,
+              amount_cents: 0,
+              created_at: current_time - 2.seconds
+            )
+          end
+          let(:params) { super().tap { |request_body| request_body.first["fees"] = [request_body.first["fees"].first] } }
+
+          it "excludes it from the request" do
+            service_call
+
+            expect(WebMock).to have_requested(:post, endpoint).with(body: params.to_json)
+          end
+        end
+
+        context "when no fee has an amount" do
+          let(:fee_add_on) do
+            create(
+              :fee,
+              invoice:,
+              add_on:,
+              amount_cents: 0,
+              created_at: current_time - 3.seconds
+            )
+          end
+          let(:fee_add_on_two) do
+            create(
+              :fee,
+              invoice:,
+              add_on: add_on_two,
+              amount_cents: 0,
+              created_at: current_time - 2.seconds
+            )
+          end
+
+          it "reports no fee taxes without calling the provider" do
+            result = service_call
+
+            expect(result).to be_success
+            expect(result.fees).to eq([])
+            expect(WebMock).not_to have_requested(:post, endpoint)
+          end
+        end
+
         context "when special rules applied" do
           let(:body) do
             parsed_body = JSON.parse(base_body)

spec/services/integrations/aggregator/taxes/invoices/create_service_spec.rb

@@ -139,6 +139,54 @@
         it "does not create integration resource" do
           expect { service_call }.not_to change { invoice.reload.integration_resources.count }
         end
+
+        context "when a fee has no amount" do
+          let(:fee_add_on_two) do
+            create(
+              :fee,
+              invoice:,
+              add_on: add_on_two,
+              amount_cents: 0,
+              created_at: current_time - 2.seconds
+            )
+          end
+          let(:params) { super().tap { |body| body.first["fees"] = [body.first["fees"].first] } }
+
+          it "excludes it from the request" do
+            service_call
+
+            expect(WebMock).to have_requested(:post, endpoint).with(body: params.to_json)
+          end
+        end
+
+        context "when no fee has an amount" do
+          let(:fee_add_on) do
+            create(
+              :fee,
+              invoice:,
+              add_on:,
+              amount_cents: 0,
+              created_at: current_time - 3.seconds
+            )
+          end
+          let(:fee_add_on_two) do
+            create(
+              :fee,
+              invoice:,
+              add_on: add_on_two,
+              amount_cents: 0,
+              created_at: current_time - 2.seconds
+            )
+          end
+
+          it "reports no fee taxes without calling the provider" do
+            result = service_call
+
+            expect(result).to be_success
+            expect(result.fees).to eq([])
+            expect(WebMock).not_to have_requested(:post, endpoint)
+          end
+        end
       end
 
       context "when Avalara taxes are successfully fetched for finalized invoice" do
@@ -216,6 +264,25 @@
           expect { service_call }.to change { invoice.reload.integration_resources.count }.by(1)
         end
 
+        context "when a fee has no amount" do
+          let(:fee_add_on_two) do
+            create(
+              :fee,
+              invoice:,
+              add_on: add_on_two,
+              amount_cents: 0,
+              created_at: current_time - 2.seconds
+            )
+          end
+          let(:params) { super().tap { |body| body.first["fees"] = [body.first["fees"].first] } }
+
+          it "excludes it from the request" do
+            service_call
+
+            expect(WebMock).to have_requested(:post, endpoint).with(body: params.to_json)
+          end
+        end
+
         context "when invoice is voided" do
           let(:params) do
             [