This seems to be creating all sorts of problems for people.
1. Create your new gateway
2. Link to your old gateway
3. Port your existing clients across (sometimes problems if they were authorised by a paper 64-8 instead of online) (No, you can’t see the full list as the bigger firms didn’t want all their clients displayed to all their staff)
4. Set up each client for MTD for VAT but watch the timing of direct debits eg March VAT DD is due mid May. If you move to MTD before then the DD is not recognised/collected (yes, it’s daft but just work around it for one month)
Give it a try and let me know how you get on
Update: apparently HMRC can now handle the seamless transfer of the direct debits