fix

apps/edr-freight-api/src/modules/first-mile/first-mile-invoice.service.ts

@@ -1,4 +1,4 @@
-import { Injectable, Logger } from '@nestjs/common';
+import { BadRequestException, Injectable, Logger } from '@nestjs/common';
 import { OnEvent } from '@nestjs/event-emitter';
 import { Freight } from '@edr/types';
 
@@ -66,13 +66,37 @@ export class FirstMileInvoiceService {
       return null;
     }
 
+    // Reject mixed-currency truck sets — a single invoice can only be one
+    // currency, and amounts across currencies can't be summed.
+    const billableTrucks = (record.vehicleAssignments ?? []).filter(
+      (a) => Number(a.distanceKm) > 0,
+    );
+    const currencies = [
+      ...new Set(
+        billableTrucks
+          .map((a) => (a.vehicle as { currency?: string } | undefined)?.currency)
+          .filter((c): c is string => Boolean(c)),
+      ),
+    ];
+    if (currencies.length > 1) {
+      throw new BadRequestException(
+        `Cannot generate invoice: assigned trucks use mixed currencies (${currencies.join(', ')}). Assign trucks that share one currency.`,
+      );
+    }
+
+    // Currency follows the truck (price/km is quoted per vehicle), falling back
+    // to the booking's currency, then ETB.
+    const truckCurrency =
+      (record.vehicle as { currency?: string } | undefined)?.currency ||
+      (record.vehicleAssignments?.[0]?.vehicle as { currency?: string } | undefined)?.currency;
+
     return this.billing.generateInvoice({
       source: 'first_mile' as Freight.InvoiceSource,
       sourceId: record.id,
       type: 'DELIVERY_FEE',
       companyId: fm.booking!.companyId,
       companyProfileId: fm.booking!.companyProfileId || '',
-      currency: fm.booking!.paymentCurrency || 'ETB',
+      currency: truckCurrency || fm.booking!.paymentCurrency || 'ETB',
       lines: [
         {
           chargeType: 'DELIVERY',

apps/edr-freight-api/src/modules/first-mile/first-mile.service.ts

@@ -640,10 +640,24 @@ export class FirstMileService {
         { distanceKm: d.distanceKm },
       );
     }
-    const total = distances.reduce((s, d) => s + (Number(d.distanceKm) || 0), 0);
+
+    // Billing is per truck: amount = Σ (truck distance × truck price/km). The
+    // per-vehicle rate + currency live on the vehicle, so we ignore the legacy
+    // FIRST_MILE flat rate and any client-sent amount. `remainingPayment` param
+    // kept only for signature back-compat.
+    void remainingPayment;
+    const assignments = await this.dataSource.manager.find(FirstMileVehicleAssignment, {
+      where: { firstMileId: id },
+      relations: { vehicle: true },
+    });
+    const total = assignments.reduce((s, a) => s + (Number(a.distanceKm) || 0), 0);
+    const amount = assignments.reduce(
+      (s, a) => s + (Number(a.distanceKm) || 0) * (Number(a.vehicle?.pricePerKm) || 0),
+      0,
+    );
     await this.firstMileRepository.update(id, {
       exactKm: total,
-      ...(remainingPayment != null ? { remainingPayment } : {}),
+      remainingPayment: amount,
     } as any);
     return this.findById(id);
   }