Add refinement to ensure metered line items have zero cost

The billing schema has been updated to include a refinement that ensures metered line items have a cost of zero. To clarify, a different line item type should be added for a flat fee in Stripe. Additionally, unnecessary verifications and logic regarding item costs have been removed from the PlanPicker and LineItemDetails components.

packages/billing/core/src/create-billing-schema.ts

@@ -72,6 +72,20 @@ export const LineItemSchema = z
       message: 'Metered line items must have a unit and tiers',
       path: ['type', 'unit', 'tiers'],
     },
+  )
+  .refine(
+    (data) => {
+      if (data.type === LineItemType.Metered) {
+        return data.cost === 0;
+      }
+
+      return true;
+    },
+    {
+      message:
+        'Metered line items must have a cost of 0. Please add a different line item type for a flat fee (Stripe)',
+      path: ['type', 'cost'],
+    },
   );
 
 export const PlanSchema = z

packages/billing/gateway/src/components/line-item-details.tsx

@@ -187,10 +187,6 @@ export function LineItemDetails(
             return <PerSeat key={item.id} />;
 
           case 'metered': {
-            if (item.cost > 0) {
-              return <FlatFee key={item.id} />;
-            }
-
             return <Metered key={item.id} />;
           }
         }

packages/billing/gateway/src/components/plan-picker.tsx

@@ -79,21 +79,6 @@ export function PlanPicker(
             }
           },
           { message: t('noPlanChosen'), path: ['planId'] },
-        )
-        .refine(
-          (data) => {
-            try {
-              const { plan } = getProductPlanPair(props.config, data.planId);
-
-              return !(plan.paymentType === 'recurring' && !data.interval);
-            } catch {
-              return false;
-            }
-          },
-          {
-            message: t('noIntervalPlanChosen'),
-            path: ['interval'],
-          },
         ),
     ),
     defaultValues: {