Hi, i did register with the 2 Thai authorities and also purchased liability insurance for a minimum of 1,000,000 baht. You have to pay a small registration fee for one of the authorities, but luckily enough i had someone in Thailand that paid it for me online. I had no issues with taking my drones (mp3 pro & mavic 3 classic) in my hand luggage. All batteries were drained to around 30% and put into lipo battery bags. Nothings was checked flying out of Heathrow and Bangkok to Phuket.