From 07b52cbb795ff74fcd3747036eefd0c780cf8d58 Mon Sep 17 00:00:00 2001
From: Taesu <166604494+bytaesu@users.noreply.github.com>
Date: Thu, 7 May 2026 00:36:52 +0900
Subject: [PATCH] fix(stripe): preserve freeTrial and internal metadata in
 `getCheckoutSessionParams` merge (#9474)

---
 .../fix-stripe-subscription-data-merge.md     |   5 +
 packages/stripe/src/routes.ts                 |   8 +-
 packages/stripe/test/stripe.test.ts           | 116 ++++++++++++++++++
 3 files changed, 125 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/fix-stripe-subscription-data-merge.md

diff --git a/.changeset/fix-stripe-subscription-data-merge.md b/.changeset/fix-stripe-subscription-data-merge.md
new file mode 100644
index 0000000000..62e507ee93
--- /dev/null
+++ b/.changeset/fix-stripe-subscription-data-merge.md
@@ -0,0 +1,5 @@
+---
+"@better-auth/stripe": patch
+---
+
+Returning a custom `subscription_data` from `getCheckoutSessionParams` no longer hides the plan's free trial in Stripe Checkout or creates duplicate local subscription rows when the `customer.subscription.created` webhook fires.
diff --git a/packages/stripe/src/routes.ts b/packages/stripe/src/routes.ts
index fe88250ef7..f88763f57e 100644
--- a/packages/stripe/src/routes.ts
+++ b/packages/stripe/src/routes.ts
@@ -1124,8 +1124,12 @@ export const upgradeSubscription = (options: StripeOptions) => {
 							// Additional line items (metered prices, add-ons, etc.)
 							...(plan.lineItems ?? []),
 						],
+						mode: "subscription",
+						client_reference_id: referenceId,
+						...params?.params,
 						subscription_data: {
 							...freeTrial,
+							...params?.params?.subscription_data,
 							metadata: subscriptionMetadata.set(
 								{
 									userId: user.id,
@@ -1136,10 +1140,6 @@ export const upgradeSubscription = (options: StripeOptions) => {
 								params?.params?.subscription_data?.metadata,
 							),
 						},
-						mode: "subscription",
-						client_reference_id: referenceId,
-						...params?.params,
-						// metadata should come after spread to protect internal fields
 						metadata: subscriptionMetadata.set(
 							{
 								userId: user.id,
diff --git a/packages/stripe/test/stripe.test.ts b/packages/stripe/test/stripe.test.ts
index 9949d5539c..3f660d696c 100644
--- a/packages/stripe/test/stripe.test.ts
+++ b/packages/stripe/test/stripe.test.ts
@@ -8666,4 +8666,120 @@ describe("stripe", () => {
 			expect(meteredItem).not.toHaveProperty("quantity");
 		});
 	});
+
+	/**
+	 * @see https://github.com/better-auth/better-auth/issues/9129
+	 * @see https://github.com/better-auth/better-auth/issues/9130
+	 */
+	describe("getCheckoutSessionParams subscription_data merge", () => {
+		const trialOptions = {
+			...stripeOptions,
+			subscription: {
+				enabled: true,
+				plans: [
+					{
+						priceId: process.env.STRIPE_PRICE_ID_1!,
+						name: "starter",
+						lookupKey: "lookup_key_123",
+						freeTrial: { days: 14 },
+					},
+				],
+				getCheckoutSessionParams: async () => ({
+					params: {
+						payment_method_collection: "if_required" as const,
+						subscription_data: {
+							trial_settings: {
+								end_behavior: {
+									missing_payment_method: "cancel" as const,
+								},
+							},
+						},
+					},
+				}),
+			},
+		} satisfies StripeOptions;
+
+		it("preserves plan freeTrial when getCheckoutSessionParams returns custom subscription_data", async () => {
+			const { client, sessionSetter } = await getTestInstance(
+				{
+					database: memory,
+					plugins: [stripe(trialOptions)],
+				},
+				{
+					disableTestUser: true,
+					clientOptions: {
+						plugins: [stripeClient({ subscription: true })],
+					},
+				},
+			);
+
+			const email = "trial-merge@email.com";
+			await client.signUp.email({ ...testUser, email }, { throw: true });
+			const headers = new Headers();
+			await client.signIn.email(
+				{ ...testUser, email },
+				{ throw: true, onSuccess: sessionSetter(headers) },
+			);
+
+			mockStripe.checkout.sessions.create.mockClear();
+			await client.subscription.upgrade({
+				plan: "starter",
+				fetchOptions: { headers },
+			});
+
+			expect(mockStripe.checkout.sessions.create).toHaveBeenCalledWith(
+				expect.objectContaining({
+					subscription_data: expect.objectContaining({
+						trial_period_days: 14,
+						trial_settings: {
+							end_behavior: { missing_payment_method: "cancel" },
+						},
+					}),
+				}),
+				undefined,
+			);
+		});
+
+		it("preserves internal subscription metadata when getCheckoutSessionParams returns custom subscription_data", async () => {
+			const { client, sessionSetter } = await getTestInstance(
+				{
+					database: memory,
+					plugins: [stripe(trialOptions)],
+				},
+				{
+					disableTestUser: true,
+					clientOptions: {
+						plugins: [stripeClient({ subscription: true })],
+					},
+				},
+			);
+
+			const email = "metadata-merge@email.com";
+			await client.signUp.email({ ...testUser, email }, { throw: true });
+			const headers = new Headers();
+			await client.signIn.email(
+				{ ...testUser, email },
+				{ throw: true, onSuccess: sessionSetter(headers) },
+			);
+
+			mockStripe.checkout.sessions.create.mockClear();
+			await client.subscription.upgrade({
+				plan: "starter",
+				fetchOptions: { headers },
+			});
+
+			expect(mockStripe.checkout.sessions.create).toHaveBeenCalledWith(
+				expect.objectContaining({
+					subscription_data: expect.objectContaining({
+						metadata: expect.objectContaining({
+							subscriptionId: expect.any(String),
+							userId: expect.any(String),
+							referenceId: expect.any(String),
+						}),
+					}),
+				}),
+				undefined,
+			);
+		});
+	});
 });