Magento – Failed to load API definition error in magento 2 swagger

It seems that after authenticating and adding the API key on the top we can get all methods.

However, the error displayed on the botton is because the ajax request to online.swagger.io returns the error. It's because, the service can't reach your local environment. So, it's not a real error.

As previously mentioned here, to authenticate and get the api key, that will allow you to see all the available methods, just make a POST to /rest/V1/integration/admin/token with your credentials (as described here).

I.e.:

curl -X POST \
https://magento222.local.com.br/rest/V1/integration/admin/token \
  -H 'Content-Type: application/json' \
  -d '{"username": "myAdminLogin","password":"myAdminPass"}'

Swagger try to generate documentation from class annotation.

You use array as API type.

It is not support by Magento swagger implementation.

You can try to use anyType as a workaround or create your custom type.

Reference :

\Magento\Framework\Reflection\TypeProcessor

Allowed base type :

/**#@+
 * Normalized type constants
 */
const NORMALIZED_STRING_TYPE = 'string';
const NORMALIZED_INT_TYPE = 'int';
const NORMALIZED_FLOAT_TYPE = 'float';
const NORMALIZED_DOUBLE_TYPE = 'double';
const NORMALIZED_BOOLEAN_TYPE = 'boolean';
const NORMALIZED_ANY_TYPE = 'anyType';

You can also add array type but you need to do some custom development.

If your website is different than default, you will need to change the form URL hidden value to match your website.