Starting point:

You want to conclude a shared hosting contract and want to "fill" the inclusive domains in this shared hosting contract with multiple domains that are registered at another provider?

Procedure:

1.)
Specify, which one of the existing domains is supposed to be the future main domain.

2.)
Order the desired shared host package on our website. Pay attention that you can manage at least 2 or more domains in the package. Specify the chosen main domain during the ordering process so it can be moved at the same time.

3.)

After the shared hosting package has been set up and the main domain has been moved, the shared host already works with the main domain.
Now transfer the other domains via the customer center as "co-domain" in your shared host contract and intrude the moving the domain on the shared host afterwards.

Done.