API overview

The Byl API lets you manage invoices, checkouts, customers, and subscriptions directly from your own system. The API follows REST principles, accepting and returning data as JSON.

Quick test

1. Create a project API token.
2. Copy your project ID.
3. Run the request below, then open the url in the response to try the payment flow.

BYL_PROJECT_ID="your project ID"
BYL_TOKEN="your API token"

curl -X POST https://byl.mn/api/v1/projects/$BYL_PROJECT_ID/invoices \
    -H "Authorization: Bearer $BYL_TOKEN" \
    -H 'Accept: application/json' \
    -H 'Content-Type: application/json' \
    -d '{ "amount": 1000, "description": "My first invoice" }'

Tip

While your project is in Test mode, the API works exactly the same, and transactions are limited to ₮100. See Test and Live for details.

Base URL

All endpoints start with:

https://byl.mn/api/v1

Authentication

Pass your API token in the Authorization header on every request:

Authorization: Bearer <your token>

A token is created from a project’s page and is valid in that project only; calling another project’s endpoint returns 403. A platform team that opens projects for its clients creates a team token, valid across every project of the team, to call the clients and projects API. See the API token page for creating and revoking tokens.

If the token is missing or invalid, the API returns 401:

{
  "message": "Unauthenticated."
}

Project ID

All project-scoped endpoints follow the /v1/projects/:id pattern. For example: GET /v1/projects/1, POST /v1/projects/1/invoices.

:id is your project’s number, shown on the project settings page in the dashboard.

In all the examples below, replace $BYL_PROJECT_ID with this number.

Request format

Method	Usage
GET	Read data. Makes no changes.
POST	Create a resource, or perform an action (e.g. void an invoice).
PUT	Update existing data.
DELETE	Delete data.

Send the request body as JSON, and always include these two headers:

Content-Type: application/json
Accept: application/json

Caution

If you forget the Accept: application/json header, error responses may come back as HTML instead of JSON.

Responses

When a single object is returned, it is wrapped in a data field:

{
  "data": {
    "id": 3,
    "status": "open",
    "amount": 1000,
    "description": "Миний эхний нэхэмжлэх",
    "project_id": 1,
    "created_at": "2026-06-24T05:27:42.000000Z",
    "updated_at": "2026-06-24T05:27:42.000000Z"
  }
}

For endpoints that return lists (for example, listing subscriptions), data is an array, accompanied by links and meta pagination information. Each page contains 25 records; fetch the next page with the ?page=2 parameter.

{
  "data": [ /* ... */ ],
  "links": {
    "first": "https://byl.mn/api/v1/projects/1/subscriptions?page=1",
    "last": "https://byl.mn/api/v1/projects/1/subscriptions?page=3",
    "prev": null,
    "next": "https://byl.mn/api/v1/projects/1/subscriptions?page=2"
  },
  "meta": {
    "current_page": 1,
    "last_page": 3,
    "per_page": 25,
    "total": 63
  }
}

Errors

HTTP code	Description
401	Token is missing, invalid, or has been revoked.
403	You are not a member of the project’s team, or the team is suspended.
404	The requested resource was not found (or belongs to another project).
409	The action is not possible in the current state (e.g. canceling an already-canceled subscription).
422	Validation error, or a business logic requirement was violated.
503	Organization setup is incomplete, or the payment provider returned an error.
5xx	Error on Byl’s side. Retry the request.

Validation errors

If a parameter is invalid or missing, the response has a 422 code and an errors field:

{
  "message": "The amount field is required.",
  "errors": {
    "amount": ["The amount field is required."]
  }
}

Business logic errors

If the parameters are valid but the action is not possible in the current state, the response has a 422 code with error and error_code fields:

{
  "error": "invalid_invoice_state",
  "error_code": 405,
  "message": "Нэхэмжлэхийн төлөв буруу."
}

error_code is an internal Byl code and is unrelated to the HTTP status. We recommend branching on the error field rather than the code.

error	error_code	Description
invalid_invoice_state	405	The invoice’s status does not allow this action (e.g. creating a payment on a paid invoice).
inactive_payment_method_type	402	This payment method is not active for the project.
invalid_payment_amount_for_pocket_driver	407	Payments via Pocket must be greater than ₮500.
closed_checkout	408	The checkout is closed (paid or expired).
checkout_cannot_be_edited	403	The checkout is in a state that cannot be edited.
invoice_subscription_state	406	The subscription’s status does not allow this action.

Organization setup errors

If your project’s setup is incomplete, or the payment provider returns an error, the response has a 503 code in the same shape:

error	error_code	How to fix
valid_subscription_required	505	An active Byl plan is required to operate in Live mode.
missing_bank_account	501	Add a bank account to the business.
missing_primary_bank_account	502	Make one of the business’s bank accounts the default.
payment_method_error	504	Temporary error on the payment provider’s side — try again.

Endpoint list

All paths below are prefixed with https://byl.mn/api/v1.

Invoices

Method	Endpoint	Description
POST	/projects/:id/invoices	Create an invoice
GET	/projects/:id/invoices/:invoice_id	Retrieve an invoice
POST	/projects/:id/invoices/:invoice_id/void	Void an invoice
DELETE	/projects/:id/invoices/:invoice_id	Delete an invoice

Checkout

Method	Endpoint	Description
POST	/projects/:id/checkouts	Create a checkout
GET	/projects/:id/checkouts/:checkout_id	Retrieve a checkout

Customers

Method	Endpoint	Description
POST	/projects/:id/customers	Create a customer
GET	/projects/:id/customers/:customer_id	Retrieve a customer
GET	/projects/:id/customers/by-client-reference-id/:ref	Retrieve by your own ID

Subscriptions

Method	Endpoint	Description
GET	/projects/:id/subscriptions	List subscriptions
POST	/projects/:id/subscriptions	Start a trial
GET	/projects/:id/subscriptions/:subscription_id	Retrieve a subscription
POST	/projects/:id/subscriptions/:subscription_id/cancel	Cancel
POST	/projects/:id/subscriptions/:subscription_id/resume	Resume a canceled subscription

Billing portal

Method	Endpoint	Description
POST	/projects/:id/billing-portal/sessions	Create a portal session

Next steps

• API token — create a token and send your first request
• Webhook — receive payment notifications in your own system
• Laravel SDK — integrate without calling the API directly if you use Laravel