Master detail - Does not display save button

I have a master-detail application (invoice) made up of three steps, the first is the header, the second the product details, the third the invoice totals.
To view the detail of the products (detail) it is necessary to save the data of the master application but the [save] button is displayed only in the last step, the total step, otherwise only the cancel button is displayed. Obviously it is neither comfortable nor intuitive.
The ideal would be that when you press the next button, on the bottom toolbar, the procedure would save the master record to make the detail edit grid appear on the next step.
Is it possible to do this? Are there other methods?
Thank you all.