Hi,
I know that there is different way to implement the Authorize.net recurring depending of the used mode. I don't know which Authorize API you are using (AIM maybe ?). But it will require some specific development in order to improve the actual plugin.
Akeeba embedded some recurring payment plugin but there are not compatible with HikaShop which is using different trigger and features.
After that, the 45 day "trial" is like the recurring, it as to be implemented in the plugin if you want to have some kind of option in the plugin configuration. I know that is it possible with Authorize CIM (with some "trick") but I don't remember if the other API propose such feature.
But once again, it is some specific development, it require some time for the analyze and for the implementation.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.