Ubercart 3.1 causing fatal error on checkout

Only payment method is uc_monerishpp. Add item to a cart, go to checkout.

Fatal error: Unsupported operand types in REDACTED/sites/all/modules/ubercart/payment/uc_payment/uc_payment_checkout_pane.inc on line 83

This is what's throwing it:

      $func = _uc_payment_method_data($order->payment_method, 'callback'); 
      if (function_exists($func) && $details = $func('cart-details', $order, $form, $form_state)) { 
        unset($contents['details']['#markup']); 
        $contents['details'] += $details; // This is the line 83 
      }

The problem: function uc_payment_method_monerishpp op cart-details is returning a string, not an array.