It's possible to integrate the extension Akeeba Subscriptions into ccInvoices, in the sense that a new subscription in Akeeba Subscriptions can trigger the creation of an invoice in ccInvoices. When using this integration there are a few things you should be aware off.

Not required reading: a background

The issue is mostly that ccInvoices was not developed with the Akeeba Subscriptions integration in mind. When the integration was developed by Akeeba, we had already made decisions about for example the ccInvoices database structure, which would prove difficult to change without a larger rewrite of ccInvoices. We will however do a further investigation into how we can improve the integration from our end in a future version, and consider implementing these changes. For now, anyone using the integration should be aware of the below, to use ccInvoices and Akeeba Subscriptions in the most optimal setting. 

Documentation

Akeeba Subscriptions - ccInvoices integration

Akeeba Subscriptions - ccInvoices tags

1) Invoice discount

ccInvoices only supports the option to add a discount in percentages (eg. 2% discount) and not in amounts. Akeeba Subscriptions also supports the option for a discount in amounts (eg. 2 euro's). If an amount discount is communicated to ccInvoices via the integration plugin, it is possible this is shown as a percentage. The solution is to use the "ccInvoices tags" option from Akeeba Subscription and use the tag "{asubs_discount_amount}" specifically.

Read more about the Akeeba Subscriptions - ccInvoices tags plugin

2) Invoice # format

If you use the Akeeba Subscriptions integration, you can not use the "Invoice # format" in the ccInvoices configuration to create a custom invoice number. You must stick to a regular invoice number, for example: 001, 002, 003. The only way to use the "Invoice # format" is to fork the Akeeba Subscription integration plugin and adjust it to support your particular case. 

3) Replace default tags

Akeeba Subscriptions registers order/subscription data that you might want to add to the ccInvoices "Invoice PDF" template with the "ccInvoices tags" option from Akeeba Subscriptions. This will improve the usefullness of the invoice sent to your customers. For example, you might want to replace {item_name} with {aslevel_title}.

Read more about the Akeeba Subscriptions - ccInvoices tags plugin.

4) Reset invoice numbers

The "Reset invoice numbers" function in the ccInvoices configuration currently only resets invoice numbers in ccInvoices itself (without deleting previous invoices), but does not do so in Akeeba Subscriptions. Therefor, invoices created in ccInvoices will have the invoice number reset, invoices created via the Akeeba Subscriptions integration plugin will not. If you want to also reset the invoice numbers for invoices created via the Akeeba Subscriptions integration, you will need to do modification in your Joomla! database. First click the "Reset invoice numbers" button in the ccInvoices configuration, then go to PHPMyAdmin, open table "#__akeebasubs_invoices" and remove all records.