<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="Magento\Sales\Api\Data\ShipmentInterface">
        <attribute code="order_increment_id" type="string" />
    </extension_attributes>

    <extension_attributes for="Magento\Sales\Api\Data\OrderInterface">
        <attribute code="snowio_relateddata" type="SnowIO\ExtendedSalesRepositories\Api\Data\OrderRelatedDataInterface[]" />
    </extension_attributes>

    <extension_attributes for="Magento\Sales\Api\Data\CreditmemoItemInterface">
        <attribute code="back_to_stock" type="boolean" />
    </extension_attributes>
</config>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="Magento\Sales\Api\Data\ShipmentInterface">
        <attribute code="order_increment_id" type="string" />
    </extension_attributes>

    <extension_attributes for="Magento\Sales\Api\Data\OrderInterface">
        <attribute code="snowio_relateddata" type="SnowIO\ExtendedSalesRepositories\Api\Data\OrderRelatedDataInterface[]" />
    </extension_attributes>

    <extension_attributes for="Magento\Sales\Api\Data\CreditmemoItemInterface">
        <attribute code="back_to_stock" type="boolean" />
    </extension_attributes>
</config>

Add space line to xml file
Add space line to xml file
