I have added an extension attribute via
extension_attributes.xml
<?xml version="1.0" ?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
<extension_attributes for="Magento\Customer\Api\Data\AddressInterface">
<attribute code="neighborhood" type="string"/>
<attribute code="reference" type="string"/>
</extension_attributes>
<extension_attributes for="Magento\Quote\Api\Data\AddressInterface">
<attribute code="neighborhood" type="string"/>
<attribute code="reference" type="string"/>
</extension_attributes>
</config>
It shows up when using other payment methods such as OpenPay, I can even see it when making a mock order (extension attribute is at the bottom):
Does anyone know if the process to read that attribute is any different when using PayPal as a payment method?