If the auto action is set to trigger on Completed, Processed and also Pending, will it mean that it will fire twice or maybe three times ?

Yes.

One for the first pending state and the second time for the Completed state for instance ?

Correct.

and if yes how can we avoid this to get only ONE outside invoice ?

I recommend whatever you're using to generate your invoices check if the invoice already exists or not before creating it.

For instance setting first payment to 180 € and recurring ones to 144 € and using the OnCpayAfterPaymentStatusUpdate sends only 144 as payment_gross or mc_gross to our API for invoicing with the attached code.

Those will always be the amount the basket paid. You can grab the recurring amount from mc_amount3.

Does it mean that this is not the correct trigger to use ?

That event fires anytime the payment state changes for a basket. I'm guessing it's the one you need to use, but there's also onCPayUserStateChange for when a users subscription state changes. onCPayUserStateChange however doesn't come with the basket object and only has the subscription object.

Do you have news on Beat work regarding invoicing ?

No, the planned improvement is generating an invoice for recurring payments. As invoices are tied to baskets it's a massive change. I'll be honest we don't yet know the best way to approach this yet and have discussed it several times. There's massive risk in altering this behavior so we're trying to be careful about it. As the ticket for this doesn't contain private data I've moved it to the public CBSubs tracker.

forge.joomlapolis.com/issues/6647