Hi,
The "paypa"l plugin does not require application credentials. Just a paypal email is required.
The "paypal pro" plugin require application credentials (username, password, signature).
With HikaMarket we also have a "paypal adaptive" plugin which require application credentials too (email, username, password, signature).
To create a payment method configuration, you have to show your payment plugin listing and use the "new" button. Then select the payment plugin and create a configuration for it.
Our now payment system allow you to create several configuration for one payment plugin.
I don't know why HikaShop is not listed, we will see to contact them in order to fix it. We have several payment plugins integrated in HikaShop are they are working well.
Regards,