API Migration

Current source does not register the old route POST /api/v1/order/create-transaction.

It also does not register the old compatibility route POST /payments/epusdt/v1/order/create-transaction.

Replace old integrations with one of these live routes

Use case	Current live route
Native JSON API (recommended)	POST /payments/gmpay/v1/order/create-transaction
Redirect / EPay-style flow	GET/POST /payments/epay/v1/order/create-transaction/submit.php

Important migration changes

1. Every incoming order request must identify the merchant with pid.
2. Signature verification uses the secret_key of the matching api_keys row, not an old global route-specific key.
3. Supported networks/tokens are admin-driven, so query /payments/gmpay/v1/config and read data.supported_assets instead of assuming a fixed list.
4. EPay defaults now come from admin settings (epay.default_token, epay.default_currency, epay.default_network), not from deprecated env keys like epay_pid / epay_key.