Opayo Magento 1 Installation Guide
Post Installation notes
After you install the module, you will have to set it up this is pretty easy but there are a few things that you need to know.
Our module implements all Opayo Integrations SERVER, FORM, DIRECT, PayPal, also REPEAT payments are available for backend orders.
You will see that there are some integrations that only work for backend payments, orders created on Magento's admin panel, these integrations are labeled with the word "Backend". This means that the settings are only for backend payments and wont affect frontend transaction, for example you can use two different vendornames, one for the frontend and one for moto orders (moto stands for Mail/Telephone order, this is how Opayo names backend orders)
You will find on this wiki site a section that specifically details all the settings that our module has and what do they mean.
Regarding which integration you should choose, you must know that you need to be pci dss compliant, the level varies depending on which integration you are using. Here you can read more information on this matter. The most used integration is the SERVER inFrame.