Hi Deciofigueira's,
We had requirement to create invoices in Dynamics 365 for sales and send in Financials.
As you are probably aware that OOB integration options do not offer above.
After initial setup (i.e. currency, products etc) Dynamics 365 for financial's price list governs prices and products/items in Dynamics 365 for Sales.
So I wrote a plugin that is based on Invoice and Invoice Lines Entity.
I added a custom button in invoice section> which triggers custom action > which invokes plugin.
For each/individual invoice plugin calls invoice header and collates lines (items) with appropriate prices, discount etc.
I included Dynamics 365 for Financials webservice in my solution which created NAV classes/functions, and using that I am posting invoices into Financials. The calculation of figures etc is also fine.
Note: that I delete original invoice created in Dynamics 365 for Sales as that's just used as a shell to gather invoice data and send to Financials. Once generated invoice is Posted in Financials it sends/creates a copy of the invoice in Dynamics 365 for Sales (is what you want to keep/maintain).
Let me know if you want me paste code snippet here.