AIO PayPal Plugin "Payment Pro" Setup

[WebStuff]

Can someone do a "walk-through" of the setup for AIO PayPal plugin for the Payments Pro option. Preferably if you've set this up for a UK store (whether that makes any difference).
I cannot get this working for the life of me.

I've really been struggling with this as the documentation is woefully outdated and points to URLs and pages on PayPal servers that don't exist anymore.
Even the PayPal documentation is outdated as they have links to wording that has changed or, again, disappeared completely.
A lot of them have images of pages and buttons to click, boxes to fill-in or codes to copy/paste that are the old versions which again have changed or don't exist anymore.

A simple explanation of the different words used by PayPal compared to the plugin titles would also be useful e.g. is "Secret" equivalent of "Signature" or "Password" titles .
Where to find the current values for API Username, API Password, API Signature on the CURRENT PayPal Account pages
Also correct settings for API Certificate, Payflow vendor, Payflow partner

I have debugged and tested various combinations of the values I have and can still not get this to work.
Has anybody managed it? If so please can you help.
Any help greatly appreciated.

Thanks in advance.