diff --git a/src/client.ts b/src/client.ts
index 047cfe9..3c99e3c 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -1,4 +1,5 @@
 import { verifyCallback } from './callback'
+import { Currency, Language } from './enums'
 import { TransportError } from './errors'
 import type { EpointCallback, EpointResponse } from './response'
 import { buildBody, type Payload, parse } from './transport'
@@ -39,8 +40,8 @@ export class EpointClient {
     this.publicKey = options.publicKey
     this.privateKey = options.privateKey
     this.baseUrl = (options.baseUrl ?? PRODUCTION_URL).replace(/\/+$/, '')
-    this.language = options.language ?? 'az'
-    this.currency = options.currency ?? 'AZN'
+    this.language = options.language ?? Language.AZ
+    this.currency = options.currency ?? Currency.AZN
     this.successRedirectUrl = options.successRedirectUrl
     this.errorRedirectUrl = options.errorRedirectUrl
     this.timeoutMs = options.timeoutMs ?? 30_000
@@ -58,7 +59,7 @@ export class EpointClient {
       publicKey,
       privateKey,
       baseUrl: env.EPOINT_BASE_URL ?? PRODUCTION_URL,
-      language: env.EPOINT_LANGUAGE ?? 'az',
+      language: env.EPOINT_LANGUAGE ?? Language.AZ,
       successRedirectUrl: env.EPOINT_SUCCESS_REDIRECT_URL,
       errorRedirectUrl: env.EPOINT_FAILED_REDIRECT_URL,
       ...overrides,
diff --git a/src/enums.ts b/src/enums.ts
new file mode 100644
index 0000000..e5327f8
--- /dev/null
+++ b/src/enums.ts
@@ -0,0 +1,75 @@
+/** The status on a response or a callback. */
+export const Status = {
+  NEW: 'new',
+  SUCCESS: 'success',
+  FAILED: 'failed',
+  ERROR: 'error',
+  RETURNED: 'returned',
+  SERVER_ERROR: 'server_error',
+} as const
+
+export type Status = (typeof Status)[keyof typeof Status]
+
+export const SETTLED_STATUSES: ReadonlySet<string> = new Set([Status.SUCCESS])
+
+export const CardStatus = {
+  NEW: 'new',
+  ACTIVE: 'active',
+  PENDING: 'pending',
+  REJECTED: 'rejected',
+  EXPIRED: 'expired',
+  SESSION_EXPIRED: 'session_expired',
+} as const
+
+export type CardStatus = (typeof CardStatus)[keyof typeof CardStatus]
+
+export const USABLE_CARD_STATUSES: ReadonlySet<string> = new Set([CardStatus.ACTIVE])
+
+export const InvoiceStatus = {
+  WAITING: 'waiting_for_payment',
+  PAID: 'paid',
+  CANCELED: 'canceled',
+} as const
+
+export type InvoiceStatus = (typeof InvoiceStatus)[keyof typeof InvoiceStatus]
+
+export const B2BStatus = {
+  PENDING: 'PENDING',
+  PROCESSING: 'PROCESSING',
+  SUCCESS: 'SUCCESS',
+  FAILED: 'FAILED',
+} as const
+
+export type B2BStatus = (typeof B2BStatus)[keyof typeof B2BStatus]
+
+/** What the transaction did, as it comes back on a callback. */
+export const OperationCode = {
+  CARD_REGISTRATION: '001',
+  PAYMENT: '100',
+  REGISTRATION_WITH_PAYMENT: '200',
+} as const
+
+export type OperationCode = (typeof OperationCode)[keyof typeof OperationCode]
+
+export const Language = {
+  AZ: 'az',
+  EN: 'en',
+  RU: 'ru',
+} as const
+
+export type Language = (typeof Language)[keyof typeof Language]
+
+export const Currency = {
+  AZN: 'AZN',
+  USD: 'USD',
+  EUR: 'EUR',
+  RUB: 'RUB',
+} as const
+
+export type Currency = (typeof Currency)[keyof typeof Currency]
+
+/** Checkout takes any of these. */
+export const SUPPORTED_CURRENCIES: ReadonlySet<string> = new Set(Object.values(Currency))
+
+/** Split, pre-auth, refund, reverse, payout and wallet take AZN and nothing else. */
+export const AZN_ONLY: ReadonlySet<string> = new Set([Currency.AZN])
diff --git a/src/index.ts b/src/index.ts
index 7bc3b61..50e1a53 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,18 @@
 export { verifyCallback } from './callback'
 export { EpointClient } from './client'
+export {
+  AZN_ONLY,
+  B2BStatus,
+  CardStatus,
+  Currency,
+  InvoiceStatus,
+  Language,
+  OperationCode,
+  SETTLED_STATUSES,
+  Status,
+  SUPPORTED_CURRENCIES,
+  USABLE_CARD_STATUSES,
+} from './enums'
 export { EpointError, GatewayError, SignatureError, TransportError } from './errors'
 export { type EpointCallback, EpointResponse } from './response'
 export type {
diff --git a/src/response.ts b/src/response.ts
index 53a2078..aa41f08 100644
--- a/src/response.ts
+++ b/src/response.ts
@@ -1,3 +1,5 @@
+import { SETTLED_STATUSES } from './enums'
+
 function asString(value: unknown): string | undefined {
   return value === undefined || value === null ? undefined : String(value)
 }
@@ -10,7 +12,7 @@ export class EpointResponse {
   }
 
   get ok(): boolean {
-    return this.raw.status === 'success'
+    return SETTLED_STATUSES.has(String(this.raw.status))
   }
 
   get transaction(): string | undefined {
@@ -62,7 +64,7 @@ export function toCallback(raw: Record<string, unknown>): EpointCallback {
     cardName: (raw.card_name as string | null) ?? null,
     amount: raw.amount == null ? 0 : Number(raw.amount),
     otherAttr: raw.other_attr,
-    ok: status === 'success',
+    ok: SETTLED_STATUSES.has(status),
     raw,
   }
 }
diff --git a/src/transport.ts b/src/transport.ts
index 9a35918..cc68367 100644
--- a/src/transport.ts
+++ b/src/transport.ts
@@ -1,3 +1,4 @@
+import { Status } from './enums'
 import { GatewayError, TransportError } from './errors'
 import { EpointResponse } from './response'
 import { encodePayload, sign } from './signing'
@@ -27,7 +28,7 @@ export function parse(statusCode: number, body: unknown): EpointResponse {
   }
 
   const record = body as Payload
-  if (record.status === 'error') {
+  if (record.status === Status.ERROR) {
     throw new GatewayError(String(record.message ?? 'request refused'), {
       code: record.code == null ? undefined : String(record.code),
       status: String(record.status),
diff --git a/test/enums.test.ts b/test/enums.test.ts
new file mode 100644
index 0000000..ade1dda
--- /dev/null
+++ b/test/enums.test.ts
@@ -0,0 +1,17 @@
+import { describe, expect, it } from 'vitest'
+import { Currency, EpointResponse, Language, OperationCode, Status } from '../src/index'
+
+describe('enums', () => {
+  it('are plain strings on the wire', () => {
+    expect(JSON.stringify({ language: Language.AZ, currency: Currency.AZN })).toBe(
+      '{"language":"az","currency":"AZN"}',
+    )
+    expect(OperationCode.PAYMENT).toBe('100')
+    expect(Status.SERVER_ERROR).toBe('server_error')
+  })
+
+  it('still reads a raw status string as ok', () => {
+    expect(new EpointResponse({ status: 'success' }).ok).toBe(true)
+    expect(new EpointResponse({ status: 'failed' }).ok).toBe(false)
+  })
+})