Hello hardy
I therefore tried to sign them up for VAT for MTD first as an agent and got a message saying I can not sign this client up as I am not authorised to act for them so I am going round in circles.
This process will only work if your client exists within your new Agent services account - in theory within your new agent services account there is the magic button your press that will copy all your existing clients that are within your old gateway into the new gateway. i have been told once this button is pressed future synching should be automatic from old to new.
The first problem is that no list exists within the new ASA account so there is no way to check if you client is within the gateway.
Providing the client exists in the old gateway and you have merged two gateways together then you should be able to follow the process to signup the client for mtd
link for signup for agents via this page
https://www.gov.uk/guidance/sign-up-for-making-tax-digital-for-vat
Another likely problem you will find is that links take you to the wrong webpage - you may need to use in private mode or different browser to your normal browser so links take you to correect signup link rather than.
all a complete shambles and complaints should be submitted to appropriate departments / bodies that the whole process is a shambles - its not so bad when you know how to do it and it is working but it should work and and be simple and it aint.
Other important info - the minute you transfer client you lose the ability to setup direct debits / lose ability to do vat dereg and lose ability to view cert of registration - so i would recommend taking copy of cert of reg and ensuring vat dd position is as expected before doing the transfer. Only way to setup direct debit at present under mtd is via old school paper form or for client to do via their gateway.