To enable MOTO, please first reach out to Support as additional PCI documentation is required.
We also suggest to create a separate MOTO merchant account for your MOTO transactions.
MOTO's functionality is by default enabled on Magento's side.
To enable Pay By Mail on the Magento side, set the payment method to Yes in the Pay By Mail section in Magento. Also make sure to set up a skin and use the HMAC key in the configuration for Magento.
In order to use these methods of payment on Magento 2, you can create an order in the Magento portal: Sales > Orders > Create new order > Select or create customer > Select store > Select product > Select Pay By Mail or MOTO
For now, our Pay by Link product is not yet supported on Magento 2.