I am an individual seller and listing my product for the first time . I have no company. How should I get my LUCID registration number?

Hello there,

I am hopefully a future Amazon seller, just got my amazon sellers central account, but I am here to sell customizable product only on FBM basis. I found a link to Amazon custom registration - https://sellercentral.amazon.de/customization/manageCustomRegistration

but it leads me to a page with message -

Invalid Access

You do not have permissions to view this page

How do I get an Amazon Custom account and start selling?

Additional Q - I was planning to run ads from the very beginning, but did I just learn correctly that I can't run ads on a new account for some time?

I registered Lucid number and I would be glad if you can help me how to do the packaging process...