Find the service data object

AccountManagementInterface.php

...

/**
     * Create customer account. Perform necessary business operations like sending email.
     *
     * @api
     * @param \Magento\Customer\Api\Data\CustomerInterface $customer
     * @param string $password
     * @param string $redirectUrl
     * @return \Magento\Customer\Api\Data\CustomerInterface
     * @throws \Magento\Framework\Exception\LocalizedException
     */
    public function createAccount(
        \Magento\Customer\Api\Data\CustomerInterface $customer,
        $password = null,
        $redirectUrl = ''
    );
 
...