Hi,
Ok, I got it.
There is a difference of the data send between "chained" and "parallel" modes.
In the plugin, please replace this code:
			$full_amount = round($order->cart->full_total->prices[0]->price_value_with_tax, (int)$this->currency->currency_locale['int_frac_digits']);
			$e = array(
				'email' => $this->payment_params->email,
				'amount' => $full_amount
			);
By:
			$full_amount = round($order->cart->full_total->prices[0]->price_value_with_tax, (int)$this->currency->currency_locale['int_frac_digits']);
			if($this->payment_params->payment_mode != 'chained') {
				foreach($suborders as $k => $suborder) {
					if($suborder->order_vendor_id <= 1)
						continue;
					$full_amount -= hikashop_toFloat($suborder->order_vendor_price);
				}
			}
			$e = array(
				'email' => $this->payment_params->email,
				'amount' => $full_amount
			);It will fix the amount value in the parallel mode.
This part of code was commented in my plugin because it generated an error in chained payment. But I didn't realized that it was still useful in parallel mode.
Thanks for the feedback !
PS: I will update the package as soon as possible