How to get terms and condition input field to appear on WooCommerce checkout page?

If you can not process payments due to missing terms and condition form field, you can try to add this field yourself or unlink the field from WooCommerce setting panel. If you unlink the terms, at least try to add a link with information on that page for your users (as this is usually required by law).

<?php
// Add term and conditions check box on registration form
add_action( 'woocommerce_register_form', 'add_terms_and_conditions_to_registration', 20 );
function add_terms_and_conditions_to_registration() {

    if ( wc_get_page_id( 'terms' ) > 0 && is_account_page() ) {
        ?>
        <p class="form-row terms wc-terms-and-conditions">
            <label class="woocommerce-form__label woocommerce-form__label-for-checkbox checkbox">
                <input type="checkbox" class="woocommerce-form__input woocommerce-form__input-checkbox input-checkbox" name="terms" <?php checked( apply_filters( 'woocommerce_terms_is_checked_default', isset( $_POST['terms'] ) ), true ); ?> id="terms" /> <span><?php printf( __( 'I&rsquo;ve read and accept the <a href="%s" target="_blank" class="woocommerce-terms-and-conditions-link">terms &amp; conditions</a>', 'woocommerce' ), esc_url( wc_get_page_permalink( 'terms' ) ) ); ?></span> <span class="required">*</span>
            </label>
            <input type="hidden" name="terms-field" value="1" />
        </p>
    <?php
    }
}

// Validate required term and conditions check box
add_action( 'woocommerce_register_post', 'terms_and_conditions_validation', 20, 3 );
function terms_and_conditions_validation( $username, $email, $validation_errors ) {
    if ( ! isset( $_POST['terms'] ) )
        $validation_errors->add( 'terms_error', __( 'Terms and condition are not checked!', 'woocommerce' ) );

    return $validation_errors;
}

If you unlink the terms page, the error message will not appear. Read more here:

https://stackoverflow.com/questions/49311826/add-a-terms-and-conditions-checkbox-in-woocommerce-registration-form