> ## Documentation Index > Fetch the complete documentation index at: https://docs.fynn.eu/llms.txt > Use this file to discover all available pages before exploring further. # Create a payment plan > Split an open, finalized invoice into installments. Send EITHER an explicit `installments` array OR a `split` object, never both and never neither. The installment amounts (or the computed split) must sum to the current open amount of the invoice in cents. In split mode the rounding remainder is added to the last installment. The invoice must be finalized and open (not draft, paid, canceled or refunded) and must not already have an active plan. While the plan is active, dunning for the invoice is paused. ## OpenAPI ````yaml assets/openapi-v2-payment-plans.json post /api/payment-plans openapi: 3.1.0 info: title: Fynn V2 Payment Plans API version: 2026-07 description: >- REST API for Fynn payment plans (Zahlungsplan). Split an open invoice into interest-free installments while dunning stays paused, let Fynn collect direct-debit installments automatically, and react to the plan lifecycle over webhooks. All amounts are integers in the smallest currency unit (cents). Authenticate with an Organisation API token. servers: - url: https://coreapi.io description: Production - url: https://preview.coreapi.io description: Sandbox security: - ApiToken: [] tags: - name: Payment Plans description: Create, read, cancel and extend the installment plan of an open invoice. paths: /api/payment-plans: post: tags: - Payment Plans summary: Create a payment plan description: >- Split an open, finalized invoice into installments. Send EITHER an explicit `installments` array OR a `split` object, never both and never neither. The installment amounts (or the computed split) must sum to the current open amount of the invoice in cents. In split mode the rounding remainder is added to the last installment. The invoice must be finalized and open (not draft, paid, canceled or refunded) and must not already have an active plan. While the plan is active, dunning for the invoice is paused. operationId: createPaymentPlan requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/CreatePaymentPlanInput' responses: '201': description: The created payment plan. content: application/json: schema: $ref: '#/components/schemas/PaymentPlan' '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/Forbidden' '422': $ref: '#/components/responses/UnprocessableEntity' components: schemas: CreatePaymentPlanInput: type: object description: Send EITHER installments OR split, never both and never neither. properties: invoiceId: type: string format: uuid description: The open, finalized invoice to split. example: 10000000-0000-0000-0003-000000000001 paymentMethodId: type: string format: uuid nullable: true description: >- Payment method used for direct-debit collection. Defaults to the invoice payment method, with the customer default as fallback. Must belong to the invoice customer. example: null installments: type: array description: >- Manual mode. Explicit installments with due dates and amounts, in ascending order, summing to the open amount in cents. items: $ref: '#/components/schemas/InstallmentInput' split: $ref: '#/components/schemas/SplitInput' sendEmail: type: boolean default: true description: >- Whether the customer receives the schedule-overview email when the plan is created. Set false to create the plan silently. required: - invoiceId PaymentPlan: type: object properties: id: type: string format: uuid example: 10000000-0000-0000-00e0-000000000001 invoiceId: type: string format: uuid example: 10000000-0000-0000-0003-000000000001 status: $ref: '#/components/schemas/PlanStatus' totalAmount: type: integer description: >- Sum of all installments in cents. Equals the open amount at creation. example: 1190 currencyCode: type: string example: EUR paymentMethodId: type: string format: uuid nullable: true example: 10000000-0000-0000-004f-000000000001 createdAt: type: string format: date-time example: '2026-07-05T16:20:00+00:00' completedAt: type: string format: date-time nullable: true description: Timestamp the plan completed (all installments paid), or null. example: null brokenAt: type: string format: date-time nullable: true description: Timestamp the plan broke, or null. example: null canceledAt: type: string format: date-time nullable: true description: Timestamp the plan was canceled, or null. example: null brokenReason: type: string nullable: true description: Reason the plan broke, or null while active. example: null installments: type: array items: $ref: '#/components/schemas/Installment' required: - id - invoiceId - status - totalAmount - currencyCode - paymentMethodId - createdAt - completedAt - brokenAt - canceledAt - brokenReason - installments InstallmentInput: type: object description: One installment in manual mode. properties: dueAt: type: string format: date description: >- Due date of the installment (Y-m-d). Must lie in the future and be strictly after the previous installment. example: '2026-08-05' amount: type: integer description: >- Installment amount in the smallest currency unit (cents). Must be positive. example: 595 required: - dueAt - amount SplitInput: type: object description: Even split of the open amount into a number of installments. properties: count: type: integer minimum: 2 maximum: 36 description: Number of installments to create. example: 3 interval: type: string description: >- Distance between due dates as {n}{D|W|M|Y}, for example 1M for one month. Defaults to 1M. pattern: ^[0-9]+[DWMY]$ default: 1M example: 1M firstDueAt: type: string format: date description: Due date of the first installment (Y-m-d). Must lie in the future. example: '2026-08-05' required: - count - firstDueAt PlanStatus: type: string description: Lifecycle status of a payment plan. enum: - active - completed - broken - canceled Installment: type: object properties: id: type: string format: uuid position: type: integer description: 1-based position within the plan. example: 1 dueAt: type: string format: date description: Due date (Y-m-d). example: '2026-08-05' amount: type: integer description: Installment amount in cents. example: 595 status: $ref: '#/components/schemas/InstallmentStatus' paidAt: type: string format: date-time nullable: true description: Timestamp the installment was fully covered (ISO 8601), or null. example: null required: - id - position - dueAt - amount - status - paidAt ProblemError: type: object description: >- Problem detail error body (application/problem+json). Additional members may be present depending on the error. properties: status: type: integer example: 422 type: type: string description: Stable machine readable error key. example: PAYMENT_PLAN__SUM_MISMATCH title: type: string example: An error occurred detail: type: string example: The installments must sum to the open amount of the invoice. required: - status - type - title - detail ValidationError: type: object description: >- Validation error body (application/problem+json) returned when input fails field level validation. properties: status: type: integer example: 422 type: type: string example: https://tools.ietf.org/html/rfc2616#section-10 title: type: string example: Validation Failed violations: type: array items: type: object properties: propertyPath: type: string example: installments[0].amount message: type: string example: This value should be positive. code: type: string nullable: true required: - status - type - title - violations InstallmentStatus: type: string description: Status of a single installment. enum: - open - collecting - paid - failed responses: Unauthorized: description: Authentication is missing or the token is invalid. content: application/problem+json: schema: $ref: '#/components/schemas/ProblemError' Forbidden: description: The token is valid but lacks the required permission. content: application/problem+json: schema: $ref: '#/components/schemas/ProblemError' UnprocessableEntity: description: The request failed validation or a business rule was violated. content: application/problem+json: schema: oneOf: - $ref: '#/components/schemas/ValidationError' - $ref: '#/components/schemas/ProblemError' securitySchemes: ApiToken: type: http scheme: bearer description: >- Organisation API token. Send it as Authorization: Bearer api_... The token is scoped to a single Organisation. Reading a plan needs the invoice read permission, creating, canceling and extending need the invoice write permission. ````