Hello Yannis-specialis, thanks for posting on the Community page, Having had a look in the system we can see you have a simple start account with us that is active. One simple start if you are referring to trying to add another users you can only have one user and an accountant. That will be why it is not letting you add the user. If you are referring to adding a new customer in the customer section it should allow you to do that. Can you try clearing your cache and cookies to all time, close the browser down, reload it, log back in and try add the new customer see if that resolves it for you. If not please reach back out to us again and let us know if you're getting any error message or code coming up that's stopping you from adding this new customer.
So you can get support here or by phone or by live chat
The phone line for support is 0808 234 5337 and the line is open mon to fri 8am to 7pm
there is also live chat as well
