One Page Checkout Pro

I hope this will reach the developer of One Page Checkout Pro "bingo", as I cannot get any answer from his email or contact form.
One Page Checkout Pro is sold with the offer of free installation. This is what I would like. I have tried to do the installation myself but there is no "onecheckout" category in "modules" in the admin extensions.
My Open Cart version is 1.5.5.1 and uses Shoppica2

I can't reach the developer 2, in the mean time, have you already reached him? If it is a yes please tell me how