One of the requirements for requesting an ISA transfer from another bank/broker is to have an opened ISA with us.
On the other hand, if you have requested a previous-year transfer only and you already have an active S&S ISA elsewhere*, no deposits should be made towards your Trading 212 ISA account. You can contribute only to one S&S ISA during the same tax year.
Note: An ISA is activated whenever an amount is deposited to it during a certain tax year.