> ## Documentation Index > Fetch the complete documentation index at: https://docs.lead.bank/llms.txt > Use this file to discover all available pages before exploring further. # Applications API Validation Rules and Errors > Synchronous 422 validation responses for the Lead Applications API, covering required fields, status-specific rules, and the invalid_parameters payload. ## Overview All validation failures on the Applications API are returned synchronously. Business logic errors are returned as `422` responses with an `invalid_parameters` array that identifies which fields failed and why, so you can correct the request before retrying. ```json theme={null} { "error_type": "invalid_parameters", "error_message": "One or more parameters are invalid.", "invalid_parameters": [ { "parameter": "", "reason": "" } ] } ``` *** ## POST /v0/applications — Required Fields | Parameter | Validation Rule | Error Reason | | :------------------------- | :------------------------------------------------------ | :----------------------------------------------------------- | | `status` | Required; must be `approved`, `declined`, or `canceled` | `Status must be one of: approved, declined, canceled` | | `entities.account_holders` | Required; minimum 1 element | `Application is missing required account_holders field` | | `details` | Required object | `property "details" is missing` | | `documents` | Required array | `Application is missing required documents field` | | `decision` | Required object | `property "decision" is missing` | | `Idempotency-Key` header | Required on POST | 400 `operation_not_allowed`: `value is required but missing` | *** ## POST /v0/applications — Entity Validations (approved only) Entity ID resolution and role validation are enforced only when `status` is `approved`. | Parameter | Validation Rule | Error Reason | | :---------------------------- | :--------------------------------------------------------------------------------------------------------------------- | :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `entities.account_holders` | All entity IDs must resolve to existing entities | `expected N account holder entities but only M resolved successfully; one or more entity IDs were not found` | | `entities.authorized_signers` | All entity IDs must resolve to existing entities | `expected N authorized signer entities but only M resolved successfully; one or more entity IDs were not found` | | `entities.account_holders` | Cannot mix individual entities with business or sole\_prop entities. business and sole\_prop entities may be combined. | `account holders contain mixed entity categories; all must be individuals (consumer) or all must be business and/or sole_prop (commercial). business and sole_prop entities may be combined within the commercial category.` | | `entities.authorized_signers` | Required (min 1) when account holders are Business or Sole Prop entities | `Commercial application must have at least one authorized signer` | | `entities.authorized_signers` | Entities must have the `authorized_signer` role | `One or more authorized signer entities have incorrect role assignments` | *** ## POST /v0/applications — Field Validations | Parameter | Validation Rule | Error Reason | | :---------------------------------------------- | :---------------------------------------------------------------------------------------- | :--------------------------------------------------------------------------------------------------------------------- | | `details.credit.currency` | Must be a valid ISO 4217 currency code | `Application is missing required currency field` | | `details.credit.underwriting_grade` | Required when `status` is `approved` or `declined` for credit products | `UnderwritingGrade is required when status is approved or declined for credit products` | | `details.credit.limit` | Required when `status` is `approved` for credit products | `CreditLimit is required when status is approved for credit products` | | `details.credit.max_limit` | Required when `status` is `approved` for credit products | `MaxCreditLimit is required when status is approved for credit products` | | `details.credit.limit` | Cannot exceed `details.credit.max_limit` for approved applications | `CreditLimit must not exceed MaxCreditLimit for approved credit products` | | `details.credit.report.score` | If `report` object is provided, score is required; maximum value is 850 | `CreditScore is required with credit_pulled_at and credit_report_source, maximum value is 850` | | `details.credit.report.pulled_at` | Required when `report` object is provided | `CreditPulledAt is required with credit_score and credit_report_source, must be valid ISO8601 datetime` | | `details.credit.report.source` | Required when `report` object is provided; must be `equifax`, `experian`, or `transunion` | `CreditReportSource is required with credit_score and credit_pulled_at, must be one of: equifax, experian, transunion` | | `details.adverse_action_notice.delivered_at` | Required when `status` is `declined` | `AANDeliveredAt must be valid ISO8601 datetime when status is declined` | | `details.adverse_action_notice.reason` | Required when `status` is `declined` | `AANReason is required when status is declined` | | `details.adverse_action_notice.delivery_method` | Required when `status` is `declined`; must be `email`, `text`, or `other` | `AANDeliveryMethod must be one of: email, text, other when status is declined` | *** ## Downstream Constraints — Account Creation When you later use an approved application to create an Account, the Accounts API enforces matching between the application and the account. The rules below run on `POST /v0/accounts`, not on `POST /v0/applications`, but a mismatch will block account creation against this application — design the roster on the application accordingly. | Constraint | Validation Rule | Error Reason | | :------------------------------------- | :--------------------------------------------------------------------------------------------------------------------------------- | :--------------------------------------------------------------------------------------------------------- | | `account_holder_type` | Must match the application | Account holder type does not match the linked application | | Account holders and Authorized Signers | Must match between the application and the account on initial account creation. These may change via PATCH after account creation. | Account Holders and Authorized Signers must match between the application and account on account creation. | | Application `status` | Must be `approved` when the application is referenced as `application_id` on an account | application\_id is not linked to an approved application | See the [Accounts API validations](/api-integrations/accounts/validations#application-match-validations) for the canonical application-match rules. *** ## GET /v0/applications/id and GET /v0/applications/id/entity\_relationships | Validation | Error | | :------------------------------------------------------------------ | :---------------------------------------------------------------------------------------- | | `id` must match the pattern `^application_\w+$` | 422 `validation_error`: `string doesn't match the regular expression "^application_\w+$"` | | Application must exist | 404 `not_found`: `The requested application was not found` | | In-progress (non-terminal) applications are not retrievable via API | 404 `url_invalid`: `The requested application was not found` | *** ## Authentication | Scenario | Error | | :---------------------------------------------------------------- | :----------------------- | | Using an `application/read` token to call `POST /v0/applications` | 403 `insufficient_scope` | | Using an unrelated scope token (e.g., `account_number/read`) | 403 `insufficient_scope` | | Using an invalid or expired token | 403 `token_invalid` |