Hi,
First, please be sure that your database is up-to-date thanks to the "check database" button available in the toolbar when you are in the HikaShop configuration.
Afterwards, it would be interesting to hide the warnings by patching the plugin and adding a "@" before the variable, like :
$vars["L_TAXAMT".$i] = round(@$order->order_payment_tax, (int)$this->currency->currency_locale['int_frac_digits']);
The "paypal (classical)" plugin already have these for the order_payment_tax variables ; so I suppose that the "paypalpro" plugin has been forgotten.
We will add the patchs for the next release.
But for the last one, on "com_rsvppro", I'm afraid that we can't do anything for it.
Regards,