If you try to transfer more than £20,000 of new funds into your Zopa ISA, Investor Services will contact you to advise that you’ve gone above the annual allowance and will let you know your options.
Should you go over your allowance across multiple ISAs in one tax year, it's best to get in touch with HMRC on its ISA helpline: 0300 200 3312 (Monday to Friday 8am to 8pm, Saturday 8am to 4pm, Sunday 9am to 5pm). They'll talk you through your options as it can take a bit of untangling depending on your situation.
Remember, your allowance spans any cash ISA, stocks and shares ISA or innovative finance ISA that you've subscribed to this year.
It's important to keep track of the total amount of new funds you've put into your ISAs. If you can have this information to hand when you speak to HMRC, it'll help speed things along.