You render a commercial or artistic service for which you must issue an invoice. You have no legal entity or status allowing you to issue such an invoice. The umbrella company invoices your services to your customer on your behalf.
A work or service contract is drawn up between you and the umbrella company.
The umbrella company remunerates you, retaining 10% of the amounts invoiced as its fee
It is obvious that the complex nature of tax systems makes it impossible to provide simplistic answers to these questions.
Our job is to inform you concerning the rules of the game of international taxation, thus allowing you to make informed decisions after understanding the profitability/risk relation of the solution.