<?php

namespace OpsWay\ZohoBooks\Api;

class Invoices extends BaseApi
{
    const API_PATH = 'invoices';
    const API_KEY = 'invoice';

    public function applyCredits($invoiceId, $data)
    {
        $this->client->post(static::API_PATH.'/'.$invoiceId.'/credits', $this->organizationId, $data);

        return true;
    }

    public function markAsSent($invoiceId)
    {
        $this->client->post(static::API_PATH.'/'.$invoiceId.'/status/sent', $this->organizationId);

        return true;
    }

    public function markAsVoid($invoiceId)
    {
        $this->client->post(static::API_PATH.'/'.$invoiceId.'/status/void', $this->organizationId);

        return true;
    }
}

<?php

namespace OpsWay\ZohoBooks\Api;

class Invoices extends BaseApi
{
    const API_PATH = 'invoices';
    const API_KEY = 'invoice';

    public function applyCredits($invoiceId, $data)
    {
        $this->client->post(static::API_PATH.'/'.$invoiceId.'/credits', $this->organizationId, $data);

        return true;
    }

    public function markAsSent($invoiceId)
    {
        $this->client->post(static::API_PATH.'/'.$invoiceId.'/status/sent', $this->organizationId);

        return true;
    }

    public function markAsVoid($invoiceId)
    {
        $this->client->post(static::API_PATH.'/'.$invoiceId.'/status/void', $this->organizationId);

        return true;
    }

    /**
     * Email an invoice to the customer
     *
     * @see: https://www.zoho.com/books/api/v3/invoices/#email-an-invoice
     *
     * @param string $invoiceId
     * @param array $data
     *
     * @return bool
     */
    public function email($invoiceId, array $data = [])
    {
        $this->client->post(static::API_PATH.'/'.$invoiceId.'/email', $this->organizationId, $data);

        return true;
    }
}

Add "email an invoice" method
Add "email an invoice" method

| Q             | A
| ------------- | ---
| Branch        | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

See: https://www.zoho.com/books/api/v3/invoices/#email-an-invoice
