lifetime ISA& help to buy ISA for reassignment contract

Hi HMRC, I have recently started to purchase my first home by using the lifetime ISA/ help to buy ISA. The flat is reassignment from an assigner who initially purchased the flat with the developer for £460,000. However, they decided to withdraw the purchase and reassign the contract out. Luckily, I agreed with them to buy the flat for £420,000. My conveyancer is not sure if I am eligible for lifetime ISA& help to buy ISA as the home page only says the property costs £450,000 or less. it doesn't indicate specifically for reassignment contract where the cost should be referred to the original price or the reassignment price. As my purchase/ assignment price is is less than £450,000, I am wondering if I am able to use lifetime ISA& help to buy ISA to buy this flat?   Regards,

Hi congliu.uk,
Please see the guidance at Lifetime ISA.  It does not specify market values or sale prices.  
As long as the cost to you is below £450000, you meet that part of the criteria.  
The other criteria are you buy the property at least 12 months after you make your first payment into the Lifetime ISA, you use a conveyancer or solicitor to act for you in the purchase - the ISA provider will pay the funds directly to them and you’re buying with a mortgage.
Thank you.