As a private individual, you have the option of invoicing VAT-free in your own CPR number up to DKK 50,000 per year. That amount must of course be reported to SKAT, and you must subsequently be registered for VAT as, for example, a sole proprietorship when you cross the DKK 50,000 limit.
When you use Factofly, there is neither an upper nor a lower limit to how much you can invoice, as you are associated with Factofly as an employee in a project employment. This means that even if your earnings exceed DKK 50,000, you can continue to let Factofly handle your administration, and there is therefore no requirement to establish your own company.