conversion: more robust fbp, fbc with header-based attempt

src/lib/conversion/control.ts

@@ -113,11 +113,11 @@ export class ConversionControl {
 		const event = new ServerEvent()
 			.setEventName(eventName)
 			.setEventTime(Math.floor(Date.now() / 1000))
-			.setEventId(details.eventID)
 			.setUserData(buildUserData(details.userData))
 			.setActionSource(details.actionSource);
 
-		if (details?.eventSourceURL) event.setEventSourceUrl(details.eventSourceURL);
+		if (details.eventID) event.setEventId(details.eventID);
+		if (details.eventSourceURL) event.setEventSourceUrl(details.eventSourceURL);
 		if (params) {
 			const customData = buildCustomData(params);
 			event.setCustomData(customData);

src/lib/conversion/server.ts

@@ -8,8 +8,9 @@ import type {
 } from '$lib/types/conversion.js';
 
 import { StatusCodes } from 'http-status-codes';
+import { getFbpFbcFromCookies } from '../metapixel/fbc.ts';
 
-const getEventIP = (request: Request, getClientAddress: () => string) => {
+export const getRequestIP = (request: Request, getClientAddress: () => string) => {
 	return (
 		request.headers.get('x-forwarded-for') ||
 		request.headers.get('cf-connecting-ip') ||
@@ -26,18 +27,21 @@ const getEventIP = (request: Request, getClientAddress: () => string) => {
 export const createConversionRequestHandler: (control: ConversionControl) => RequestHandler = (
 	control
 ) => {
-	const handle: RequestHandler = async ({ request, getClientAddress }) => {
+	const handle: RequestHandler = async ({ request, getClientAddress, cookies }) => {
 		try {
 			const body = (await request.json()) as ConversionRequestBody;
 
 			// Build user data with IP and user agent
-			const ip = getEventIP(request, getClientAddress);
+			const ip = getRequestIP(request, getClientAddress);
 			const ua = request.headers.get('user-agent');
+			const { fbp, fbc } = getFbpFbcFromCookies(cookies);
 
 			const userData: ConversionUserData = {
 				...body.user,
 				ip,
-				ua: ua ?? body.user?.ua ?? undefined
+				ua: ua ?? body.user?.ua ?? undefined,
+				fbc: body.user?.fbc ?? fbc,
+				fbp: body.user?.fbp ?? fbp
 			};
 
 			// Build custom data with UTM params if applicable

src/lib/metapixel/fbc.ts

@@ -1,3 +1,4 @@
+import type { Cookies } from '@sveltejs/kit';
 import log from 'loglevel';
 
 export type EnsureFbcOptions = {
@@ -79,10 +80,19 @@ export function ensureFbc(options: EnsureFbcOptions = {}) {
 }
 
 /**
- * Helper to read both _fbp and _fbc for your CAPI payload.
+ * Helper to read both _fbp and _fbc for your CAPI payload from browser cookies.
  */
 export function getFbpFbc(): { fbp?: string; fbc?: string } {
 	const fbp = getCookie('_fbp');
 	const fbc = getCookie('_fbc');
 	return { fbp, fbc };
 }
+
+/**
+ * Helper to read both _fbp and _fbc for your CAPI payload from cookies object.
+ */
+export function getFbpFbcFromCookies(cookies: Cookies): { fbp?: string; fbc?: string } {
+	const fbp = cookies.get('_fbp') || undefined;
+	const fbc = cookies.get('_fbc') || undefined;
+	return { fbp, fbc };
+}

src/lib/types/conversion.d.ts

@@ -51,7 +51,7 @@ export type ConversionEventParams = {
  * Parameters for sending a conversion event to Meta Pixel.
  */
 export type ConversionEventDetails = {
-	eventID: string;
+	eventID?: string;
 	actionSource: 'website' | 'app' | 'offline' | 'other';
 	userData: ConversionUserData;
 	eventSourceURL?: string;