Megaventory allows you to choose which payment method will be used for the completion of an order. You can use predefined payment methods but you can also use the localization feature and add your own payment methods. Underneath you can see how the payment method feature looks like.
To add your own payment methods go to Settings > Localize > Update Specific Phrases > Your Language > Search for the specific payment method you would like to change (For example Custom Payment 1)
Or login to your account.