The list of domain present in your screen shot 1 is strange.
You just put {site_alias} and not
perhaps something using the {site_alias}
In additino, the "to site ID" also use the {site_alias}
I don't know what you expect that your customer enter in the {site_alias} parameter.
If you expect to enter a domain name, the "to site ID" and the "new DB prefix" might have problem because you will have dot (.) present in the {site_alias}.
I also noticed an inconsistency between the domain present in the list of domain using u{user_id} and the "deploy folder" that give another location {site_dir}. It should probably be {root}/multisites/u{user_id}
In addition, I notice that the "Alias link" is empty. Perhaps you may want a synonym based on the {site_alias}
As there is no specification of the expected result and requirement, I can not tell you what you should put in your setting.
All I can see is that you enter values randomly because none are consistent between each other. The URL present in the domain and the location on the disk specified in the deployed directory must match together.
Also avoid using terms in the new DB prefix that could have any character like this is the case with the {site_alias} field used in the computation of the field.