“Undefined index: interface” error from Magento 2 swagger webapi

Question

I'm getting the following error when loading the swagger routes:

Undefined index: interface in /mnt/c/develop/php/mage2/vendor/magento/module-webapi/Model/AbstractSchemaGenerator.php on line 156 {"exception":"[object] (Exception(code: 0)

I'm trying to add my own swagger endpoint. My webapi.xml looks like:

<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">

<route url="/V1/my/custom/route" method="GET">
    <service class="Vendor\Module\Api\MyInterface" method="myMethod"/>
    <resources>
        <resource ref="anonymous" />
    </resources>
</route>

What does this error mean?

Answer 1

The interface you defined, Vendor\Module\Api\MyInterface, doesn't have a method named myMethod.

Add one, clear your cache, and you should be good!