Issue:
Bug: confirm-intent API contract changes for split payments (v2)



In v2, we need to support receiving multiple payment methods in the confirm-intent request. Add a new field to support this use case

Pull request description:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [x] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
<!-- Describe your changes in detail -->
- Added `split_payment_method_data` field to `confirm-intent` call to accept a `Vec` of payment methods

<img width="502" height="763" alt="image" src="https://github.com/user-attachments/assets/69ae3cc4-3d06-4980-b2d9-52b489aa98ad" />

### Additional Changes

- [x] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application configuration/environment variables

<!--
Provide links to the files with corresponding changes.

Following are the paths where you can find config files:
1. `config`
2. `crates/router/src/configs`
3. `loadtest/config`
-->


## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd recommend starting with one first so the PR
can focus on the implementation (unless it is an obvious bug or documentation fix
that will have little conversation).
-->
Closes #9467 

## How did you test it?
<!--
Did you write an integration/unit/API test to verify the code changes?
Or did you test this change manually (provide relevant screenshots)?
-->

Note: Currently the `split_payment_method_data` field is not used. This PR just adds it to the API contract. There are no behaviour changes. The field will be used in a future PR.

Request:
```
curl --location 'http://localhost:8080/v2/payments/12345_pay_019975b06d2d77b0beff1a83df9a3377/confirm-intent' \
--header 'x-profile-id: pro_JSAAWLeyardnZ5iQDB4o' \
--header 'x-client-secret: cs_019975b06d407b738bb37971ce338246' \
--header 'Authorization: publishable-key=pk_dev_e098d9545be8466a9e52bfd7db41ec77,client-secret=cs_019975b06d407b738bb37971ce338246' \
--header 'Content-Type: application/json' \
--header 'api-key: pk_dev_e098d9545be8466a9e52bfd7db41ec77' \
--data '{
    "payment_method_data": {
        "card": {
            "card_cvc": "737",
            "card_exp_month": "03",
            "card_exp_year": "30",
            "card_number": "4000620000000007",
            "card_holder_name": "joseph Doe"
        }
    },
    "payment_method_type": "card",
    "payment_method_subtype": "card",
    "split_payment_method_data": [
        {
            "payment_method_data": {
                "gift_card": {
                    "givex": {
                        "number": "6036280000000000000",
                        "cvc": "123"
                    }
                }
            },
            "payment_method_type": "gift_card",
            "payment_method_subtype": "givex"
        }
    ],
    "browser_info": {
        "user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36",
        "accept_header": "text\\/html,application\\/xhtml+xml,application\\/xml;q=0.9,image\\/webp,image\\/apng,*\\/*;q=0.8",
        "language": "en-GB",
        "color_depth": 24,
        "screen_height": 1440,
        "screen_width": 2560,
        "time_zone": -330,
        "java_enabled": true,
        "java_script_enabled": true,
        "ip_address": "0.0.0.0"
    }
}'
```

Response:
```
{
    "id": "12345_pay_019975b06d2d77b0beff1a83df9a3377",
    "status": "succeeded",
    "amount": {
        "order_amount": 1000,
        "currency": "USD",
        "shipping_cost": null,
        "order_tax_amount": null,
        "external_tax_calculation": "skip",
        "surcharge_calculation": "skip",
        "surcharge_amount": null,
        "tax_on_surcharge": null,
        "net_amount": 1000,
        "amount_to_capture": null,
        "amount_capturable": 0,
        "amount_captured": 1000
    },
    "customer_id": "12345_cus_019975b064727f82a64abdb387d8fd72",
    "connector": "adyen",
    "created": "2025-09-23T08:28:40.634Z",
    "modified_at": "2025-09-23T08:29:32.736Z",
    "payment_method_data": {
        "billing": null
    },
    "payment_method_type": "card",
    "payment_method_subtype": "card",
    "connector_transaction_id": "GRFLWGK5NVTV7VV5",
    "connector_reference_id": "12345_att_019975b12e2176c2bfa32a42a67b8891",
    "merchant_connector_id": "mca_yON0ejlCVv7kJuPN8wRs",
    "browser_info": null,
    "error": null,
    "shipping": null,
    "billing": null,
    "attempts": null,
    "connector_token_details": null,
    "payment_method_id": null,
    "next_action": null,
    "return_url": "https://google.com/success",
    "authentication_type": "three_ds",
    "authentication_type_applied": "three_ds",
    "is_iframe_redirection_enabled": null,
    "merchant_reference_id": null,
    "raw_connector_response": null,
    "feature_metadata": null,
    "metadata": null
}
```

## Checklist
<!-- Put an `x` in the boxes that apply -->

- [x] I formatted the code `cargo +nightly fmt --all`
- [x] I addressed lints thrown by `cargo clippy`
- [x] I reviewed the submitted code
- [ ] I added unit tests for my changes where possible


Testing:


Note: Currently the `split_payment_method_data` field is not used. This PR just adds it to the API contract. There are no behaviour changes. The field will be used in a future PR.

Request:
```
curl --location 'http://localhost:8080/v2/payments/12345_pay_019975b06d2d77b0beff1a83df9a3377/confirm-intent' \
--header 'x-profile-id: pro_JSAAWLeyardnZ5iQDB4o' \
--header 'x-client-secret: cs_019975b06d407b738bb37971ce338246' \
--header 'Authorization: publishable-key=pk_dev_e098d9545be8466a9e52bfd7db41ec77,client-secret=cs_019975b06d407b738bb37971ce338246' \
--header 'Content-Type: application/json' \
--header 'api-key: pk_dev_e098d9545be8466a9e52bfd7db41ec77' \
--data '{
    "payment_method_data": {
        "card": {
            "card_cvc": "737",
            "card_exp_month": "03",
            "card_exp_year": "30",
            "card_number": "4000620000000007",
            "card_holder_name": "joseph Doe"
        }
    },
    "payment_method_type": "card",
    "payment_method_subtype": "card",
    "split_payment_method_data": [
        {
            "payment_method_data": {
                "gift_card": {
                    "givex": {
                        "number": "6036280000000000000",
                        "cvc": "123"
                    }
                }
            },
            "payment_method_type": "gift_card",
            "payment_method_subtype": "givex"
        }
    ],
    "browser_info": {
        "user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36",
        "accept_header": "text\\/html,application\\/xhtml+xml,application\\/xml;q=0.9,image\\/webp,image\\/apng,*\\/*;q=0.8",
        "language": "en-GB",
        "color_depth": 24,
        "screen_height": 1440,
        "screen_width": 2560,
        "time_zone": -330,
        "java_enabled": true,
        "java_script_enabled": true,
        "ip_address": "0.0.0.0"
    }
}'
```

Response:
```
{
    "id": "12345_pay_019975b06d2d77b0beff1a83df9a3377",
    "status": "succeeded",
    "amount": {
        "order_amount": 1000,
        "currency": "USD",
        "shipping_cost": null,
        "order_tax_amount": null,
        "external_tax_calculation": "skip",
        "surcharge_calculation": "skip",
        "surcharge_amount": null,
        "tax_on_surcharge": null,
        "net_amount": 1000,
        "amount_to_capture": null,
        "amount_capturable": 0,
        "amount_captured": 1000
    },
    "customer_id": "12345_cus_019975b064727f82a64abdb387d8fd72",
    "connector": "adyen",
    "created": "2025-09-23T08:28:40.634Z",
    "modified_at": "2025-09-23T08:29:32.736Z",
    "payment_method_data": {
        "billing": null
    },
    "payment_method_type": "card",
    "payment_method_subtype": "card",
    "connector_transaction_id": "GRFLWGK5NVTV7VV5",
    "connector_reference_id": "12345_att_019975b12e2176c2bfa32a42a67b8891",
    "merchant_connector_id": "mca_yON0ejlCVv7kJuPN8wRs",
    "browser_info": null,
    "error": null,
    "shipping": null,
    "billing": null,
    "attempts": null,
    "connector_token_details": null,
    "payment_method_id": null,
    "next_action": null,
    "return_url": "https://google.com/success",
    "authentication_type": "three_ds",
    "authentication_type_applied": "three_ds",
    "is_iframe_redirection_enabled": null,
    "merchant_reference_id": null,
    "raw_connector_response": null,
    "feature_metadata": null,
    "metadata": null
}
```

Patch:
diff --git a/crates/api_models/src/payments.rs b/crates/api_models/src/payments.rs
index 8c8052b14d0..1a035fd291e 100644
--- a/crates/api_models/src/payments.rs
+++ b/crates/api_models/src/payments.rs
@@ -2659,6 +2659,16 @@ pub struct PaymentMethodDataRequest {
     pub billing: Option<Address>,
 }
 
+#[cfg(feature = "v2")]
+#[derive(Clone, Debug, serde::Deserialize, serde::Serialize, ToSchema)]
+pub struct SplitPaymentMethodDataRequest {
+    pub payment_method_data: PaymentMethodData,
+    #[schema(value_type = PaymentMethod)]
+    pub payment_method_type: api_enums::PaymentMethod,
+    #[schema(value_type = PaymentMethodType)]
+    pub payment_method_subtype: api_enums::PaymentMethodType,
+}
+
 /// The payment method information provided for making a payment
 #[derive(Debug, Clone, serde::Deserialize, serde::Serialize, ToSchema, Eq, PartialEq)]
 pub struct RecordAttemptPaymentMethodDataRequest {
@@ -5762,6 +5772,9 @@ pub struct PaymentsConfirmIntentRequest {
     /// The payment instrument data to be used for the payment
     pub payment_method_data: PaymentMethodDataRequest,
 
+    /// The payment instrument data to be used for the payment in case of split payments
+    pub split_payment_method_data: Option<Vec<SplitPaymentMethodDataRequest>>,
+
     /// The payment method type to be used for the payment. This should match with the `payment_method_data` provided
     #[schema(value_type = PaymentMethod, example = "card")]
     pub payment_method_type: api_enums::PaymentMethod,
@@ -6083,6 +6096,7 @@ impl From<&PaymentsRequest> for PaymentsConfirmIntentRequest {
             payment_token: None,
             merchant_connector_details: request.merchant_connector_details.clone(),
             return_raw_connector_response: request.return_raw_connector_response,
+            split_payment_method_data: None,
         }
     }
 }
diff --git a/crates/openapi/src/openapi_v2.rs b/crates/openapi/src/openapi_v2.rs
index eb172cf0cf5..6ea50cb85fa 100644
--- a/crates/openapi/src/openapi_v2.rs
+++ b/crates/openapi/src/openapi_v2.rs
@@ -435,6 +435,7 @@ Never share your secret api keys. Keep them guarded and secure.
         api_models::payments::PhoneDetails,
         api_models::payments::PaymentMethodData,
         api_models::payments::PaymentMethodDataRequest,
+        api_models::payments::SplitPaymentMethodDataRequest,
         api_models::payments::MandateType,
         api_models::payments::MandateAmountData,
         api_models::payments::Card,