mismatch

I am using Typeeto to turn my MacBook Pro into a Bluetooth keyboard (but I have read it happens also with physical keyboards) and this is the issue: my MBP has a GB/English keyboard and if I set the ATV 4K language in Italian the special characters get typed (or copied&pasted) wrong, typing...

I've been given an old (circa 2008) but working MBP & I simply put in a new hard drive, increased the RAM & installed the latest OS that it would take (El Capitan 10.11.6) and I thought all was fine initially, until I realised that the Serial Number in the "About This Mac" is totally different...