Problem
PHP Notice when “SHIPTOSTATE” is not available in PayPal Express Checkout.
Undefined index: SHIPTOSTATE in /home/moddiy/public_html/modules/checkout/paypalexpress/module.paypalexpress.php at 423

Solution
In /modules/checkout/paypalexpress/module.paypalexpress.php (line 423)
Find
$stateID = $this->GetStateId($countryID, $nvpArray['SHIPTOSTATE']); $stateName = GetStateById($stateID);
Replace
//============================================= // MOD START // Fix "Undefined index: SHIPTOSTATE" error //============================================= //$stateID = $this->GetStateId($countryID, $nvpArray['SHIPTOSTATE']); //$stateName = GetStateById($stateID); if(isset($nvpArray['SHIPTOSTATE'])) { $stateID = $this->GetStateId($countryID, $nvpArray['SHIPTOSTATE']); $stateName = GetStateById($stateID); }else{ $stateID = ''; $stateName = ''; } //============================================= // MOD END //=============================================