Yes! It is possible to migrate ccInvoices information (invoices, contacts etc) from Joomla! 2.5 to Joomla! 3.x. Also read "End of Joomla! 2.5 & how to move to Joomla! 3".

We have different migration manuals for this extension:

It is very important that you install the correct version of ccInvoices in both sites!

Method 1: moving the database/files during migration

  • On the Joomla! 2.5 website:
    • create a backup of the Joomla! 2.5 website (with Akeeba Backup)
    • make sure you are using the latest version of Joomla! 2.5
    • make sure you are using the latest ccInvoices version that supports Joomla! 2.5
    • use your favorite extension to migrate your Joomla! 2.5 website (SP Upgrade) and in that extension make sure to enable the option to also move ccInvoices's database tables. SP Upgrade has this option, ask the extension developer if you can not find it. This will allow the extension to also "move" the ccInvoices information to the new Joomla! 3.x website
  • On the Joomla! 3.x website:
    • after the migration it should be enough to install the same version of ccInvoices that you had installed on Joomla! 2.5 into your Joomla! 3.x website, after which ccInvoices will recognize the database tables and work again
    • do a full check of ccInvoices to make sure everything works, for example check invoices, downloads, payment methods (if used), menu items and configuration. It might be easy to just go through the ccInvoices manual and and use that as a reference
    • it is now possible to update ccInvoices to the latest version we have available for Joomla! 3.x

Method 2: moving the database/files after migration 

For this method, experience with PHPMyAdmin (or similar) is required 
  • On the Joomla! 2.5 website:
    • create a backup of the Joomla! 2.5 website (with Akeeba Backup)
    • make sure you are using the latest version of Joomla! 2.5
    • update to/make sure you are using the latest ccInvoices version that supports Joomla! 2.5
    • login to the MySQL database of the Joomla! 2.5 website, on most hosters you can use PHPMyAdmin to reach the database, ask your hoster for details
    • find the ccInvoices tables, they start with #__ccinvoices_XXXX where #_ is a random prefix and XXXX is the table name (for example: jos_ccinvoices_invoices)
    • select all ccInvoices tables, and export them with PHPMyAdmin
  • On the Joomla! 3.x website (a migrated or new site):
    • login to the MySQL database of the Joomla! 3.x website
    • import the tables you just exported into PHPMyAdmin
    • after the migration it should be enough to install the same version of ccInvoices that you had installed on Joomla! 2.5 into your Joomla! 3.x website, after which ccInvoices will recognize the database tables and work again
    • do a full check of ccInvoices to make sure everything works, for example check invoices, downloads, payment methods (if used), menu items and configuration. It might be easy to just go through the ccInvoices manual and and use that as a reference
    • it is now possible to update ccInvoices to the latest version we have available for Joomla! 3.x