1) What is Advance Passenger Information?

You need to provide Advance Passenger Information (API) before you go on holiday if you're travelling with TUI. It's also called APIS, Secure Flight or e-Borders. In a nutshell, this is information from your passport that's required by the government of the country you're travelling to.

TUI also needs this information for Aviation Security purposes.
Flying with another airline? If your flight is with another airline then you'll need to provide your API details at check-in - you won't be able to do this before you travel.

If you're not sure who you're flying with, take a look at 'Which airline am I flying with?'