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[GH-ISSUE #9129] stripe: getCheckoutSessionParams overrides subscription_data and removes plan freeTrial #28603

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opened 2026-04-17 20:02:35 -05:00 by GiteaMirror · 1 comment
GiteaMirror commented 2026-04-17 20:02:35 -05:00
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Originally created by @mattiacerutti on GitHub (Apr 12, 2026).
Original GitHub issue: https://github.com/better-auth/better-auth/issues/9129

Is this suited for github?

  • Yes, this is suited for github

Reproduction

  1. Configure Better Auth Stripe plugin with a plan that includes a free trial:
subscription: {
  enabled: true,
  plans: [
    {
      name: "pro",
      priceId: "price_xxx",
      freeTrial: {
        days: 14,
      },
    },
  ],
}
  1. Add getCheckoutSessionParams to customize trial end behavior:
getCheckoutSessionParams: async ({ plan }) => {
  if (plan.name !== "pro") return {};

  return {
    params: {
      payment_method_collection: "if_required",
      subscription_data: {
        trial_settings: {
          end_behavior: {
            missing_payment_method: "cancel",
          },
        },
      },
    },
  };
};
  1. Trigger subscription upgrade from client:
await authClient.subscription.upgrade({
  plan: "pro",
  successUrl: "/dashboard",
  cancelUrl: "/pricing",
});

Current vs. Expected behavior

Current:

  • Stripe Checkout does not show the free trial
  • Adding subscription_data in getCheckoutSessionParams appears to overwrite the internally generated subscription_data from freeTrial

Expected:

  • subscription_data provided in getCheckoutSessionParams should be merged with internally generated values
  • The final Checkout Session should include both:
    • the free trial from plan.freeTrial
    • the custom trial_settings.end_behavior.missing_payment_method
  • Stripe Checkout should still display the free trial

What version of Better Auth are you using?

1.6.2

System info

{
  "system": {
    "platform": "darwin",
    "arch": "arm64",
    "version": "Darwin Kernel Version 25.3.0: Wed Jan 28 20:55:08 PST 2026; root:xnu-12377.91.3~2/RELEASE_ARM64_T6020",
    "release": "25.3.0",
    "cpuCount": 12,
    "cpuModel": "Apple M2 Pro",
    "totalMemory": "16.00 GB",
    "freeMemory": "0.12 GB"
  },
  "node": {
    "version": "v24.13.0",
    "env": "development"
  },
  "packageManager": {
    "name": "bun",
    "version": "1.3.6"
  },
  "frameworks": [
    {
      "name": "next",
      "version": "16.2.1"
    },
    {
      "name": "react",
      "version": "19.2.4"
    }
  ],
  "databases": [
    {
      "name": "@prisma/client",
      "version": "^7.4.2"
    }
  ],
  "betterAuth": {
    "version": "Unknown",
    "config": null,
    "error": "Converting circular structure to JSON\n    --> starting at object with constructor 'Stripe'\n    |     property 'account' -> object with constructor 'Constructor'\n    --- property '_stripe' closes the circle"
  }
}

Which area(s) are affected? (Select all that apply)

Backend

Auth config (if applicable)

Additional context

This behavior is not documented. It is unclear whether this is intentional or a bug.

Originally created by @mattiacerutti on GitHub (Apr 12, 2026). Original GitHub issue: https://github.com/better-auth/better-auth/issues/9129 ### Is this suited for github? - [x] Yes, this is suited for github ### Reproduction 1. Configure Better Auth Stripe plugin with a plan that includes a free trial: ``` subscription: { enabled: true, plans: [ { name: "pro", priceId: "price_xxx", freeTrial: { days: 14, }, }, ], } ``` 2. Add getCheckoutSessionParams to customize trial end behavior: ``` getCheckoutSessionParams: async ({ plan }) => { if (plan.name !== "pro") return {}; return { params: { payment_method_collection: "if_required", subscription_data: { trial_settings: { end_behavior: { missing_payment_method: "cancel", }, }, }, }, }; }; ``` 3. Trigger subscription upgrade from client: ``` await authClient.subscription.upgrade({ plan: "pro", successUrl: "/dashboard", cancelUrl: "/pricing", }); ``` ### Current vs. Expected behavior ## Current: - Stripe Checkout does not show the free trial - Adding `subscription_data` in `getCheckoutSessionParams` appears to overwrite the internally generated `subscription_data` from `freeTrial` ## Expected: - `subscription_data` provided in `getCheckoutSessionParams` should be merged with internally generated values - The final Checkout Session should include both: - the free trial from `plan.freeTrial` - the custom `trial_settings.end_behavior.missing_payment_method` - Stripe Checkout should still display the free trial ### What version of Better Auth are you using? 1.6.2 ### System info ```bash { "system": { "platform": "darwin", "arch": "arm64", "version": "Darwin Kernel Version 25.3.0: Wed Jan 28 20:55:08 PST 2026; root:xnu-12377.91.3~2/RELEASE_ARM64_T6020", "release": "25.3.0", "cpuCount": 12, "cpuModel": "Apple M2 Pro", "totalMemory": "16.00 GB", "freeMemory": "0.12 GB" }, "node": { "version": "v24.13.0", "env": "development" }, "packageManager": { "name": "bun", "version": "1.3.6" }, "frameworks": [ { "name": "next", "version": "16.2.1" }, { "name": "react", "version": "19.2.4" } ], "databases": [ { "name": "@prisma/client", "version": "^7.4.2" } ], "betterAuth": { "version": "Unknown", "config": null, "error": "Converting circular structure to JSON\n --> starting at object with constructor 'Stripe'\n | property 'account' -> object with constructor 'Constructor'\n --- property '_stripe' closes the circle" } } ``` ### Which area(s) are affected? (Select all that apply) Backend ### Auth config (if applicable) ```typescript ``` ### Additional context This behavior is not documented. It is unclear whether this is intentional or a bug.
GiteaMirror added the payments label 2026-04-17 20:02:35 -05:00
GiteaMirror commented 2026-04-17 20:02:36 -05:00
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@dosubot[bot] commented on GitHub (Apr 12, 2026):

Hi @mattiacerutti! I'm Dosu and I’m helping the better-auth team.

This is a confirmed bug. In routes.ts, the internal subscription_data (which includes trial_period_days from your freeTrial config) is built first, but then ...params?.params is spread after it — completely replacing subscription_data via JavaScript's shallow merge:

subscription_data: {
    ...freeTrial,  // adds trial_period_days: 14
    metadata: subscriptionMetadata.set(...),
},
...params?.params,  // your subscription_data overwrites the one above

The code already protects session-level metadata by repositioning it after the spread [1], but the same pattern is not applied to subscription_data.

Workaround: Until this is fixed, you can manually include trial_period_days in your getCheckoutSessionParams return value:

getCheckoutSessionParams: async ({ plan }) => {
  if (plan.name !== "pro") return {};
  return {
    params: {
      payment_method_collection: "if_required",
      subscription_data: {
        trial_period_days: plan.freeTrial?.days,
        trial_settings: {
          end_behavior: {
            missing_payment_method: "cancel",
          },
        },
      },
    },
  };
},

The proper fix would be to deep-merge subscription_data (similar to how metadata is handled) so internal fields like trial_period_days aren't lost when custom subscription_data is provided.

To reply, just mention @dosu.

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<!-- gh-comment-id:4231242795 --> @dosubot[bot] commented on GitHub (Apr 12, 2026): <!-- Greeting --> Hi @mattiacerutti! I'm [Dosu](https://go.dosu.dev/dosubot) and I’m helping the better-auth team. <!-- Answer --> This is a confirmed bug. In [`routes.ts`](https://github.com/better-auth/better-auth/blob/ed2c18df3150ab3a024f7d14a5b5fa58719332f2/packages/stripe/src/routes.ts#L1127-L1141), the internal `subscription_data` (which includes `trial_period_days` from your `freeTrial` config) is built first, but then `...params?.params` is spread **after** it — completely replacing `subscription_data` via JavaScript's shallow merge: ```typescript subscription_data: { ...freeTrial, // adds trial_period_days: 14 metadata: subscriptionMetadata.set(...), }, ...params?.params, // your subscription_data overwrites the one above ``` The code already protects session-level `metadata` by repositioning it after the spread [[1]](https://github.com/better-auth/better-auth/blob/ed2c18df3150ab3a024f7d14a5b5fa58719332f2/packages/stripe/src/routes.ts#L1142-L1151), but the same pattern is **not** applied to `subscription_data`. **Workaround**: Until this is fixed, you can manually include `trial_period_days` in your `getCheckoutSessionParams` return value: ```typescript getCheckoutSessionParams: async ({ plan }) => { if (plan.name !== "pro") return {}; return { params: { payment_method_collection: "if_required", subscription_data: { trial_period_days: plan.freeTrial?.days, trial_settings: { end_behavior: { missing_payment_method: "cancel", }, }, }, }, }; }, ``` The proper fix would be to deep-merge `subscription_data` (similar to how `metadata` is handled) so internal fields like `trial_period_days` aren't lost when custom `subscription_data` is provided. <!-- Dosu Comment Footer --> *To reply, just mention [@dosu](https://go.dosu.dev/dosubot?utm_source=github&utm_medium=bot-comment&utm_campaign=github-assistant&utm_content=brand-link).* --- <sup>How did I do? 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Reference: github-starred/better-auth#28603
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