Question regarding the Government Gateway and 2 separate businesses

Hi a Question regarding the Government Gateway,i got a Government Gateway account and use that to do my sole trader self-assessment stuff, but now I am a director in a Ltd start-up which is not earning any money yet, except interest, we have our utr, but it needs to be set up/registered with HMRC, i am not receiving any pay as a director, so my question is regarding the Government Gateway,I am struggling to set up a new government gateway online,it will not let me do it online and now is sending a registration code by post, do I have to use my existing government gateway and just set up through the government gateway and just set up through that the LTD company and will it not link those 2, which I do not want, as they are 2 different entity/businesses.

Hi,
You will need to contact our online services team for advice.
Technical support with HMRC online services
Thank you.