During the 2017/18 tax year, you can transfer the funds held within your Help to Buy ISA (as at the 5th April 2017) into a Lifetime ISA.
This transfer will count as a qualifying payment and will be eligible for the Government bonus. Please be aware that it will not count towards your Lifetime ISA allowance or your overall ISA allowance. If you want to transfer a Help to Buy ISA where you have made payments after 5th April 2017 you still can, however the funds that were paid in after 5th April will count towards your current Lifetime ISA subscription amount and your overall ISA allowance.
If you transfer your Help to Buy ISA to a Lifetime ISA on or after the 6 April 2018, this will be treated as a standard ISA transfer and the transfer value will count towards your current Lifetime ISA allowance.