Gravity forms: Authorize.net Invoice code

I was wondering If you knew how to add an invoice code to the forms in Authorize.net.

I check the authorize.net feed settings but they do not ask for an invoice code.Then, I started to do some research and found the hook gform_authorizenet_save_entry_id that could be used to create that invoice code.

The problem comes that there is no documentation about this hook. It was only mentioned as one of the updates. So, I’m creating a hidden field with an {entry_id} as a default value and trying to find a way to pass it as an Invoice Number.

Any help would be appreciated. Thanks ??