Problem with add zone

Hello all,
I have some problem during using api.
First, I will describe my requirements.
I want to register a lot of domains by cloudflare api. (for example 40)
For every 10 I need separate subaccount.
I thought about two options:
a) For api cloudflare create member by #account-members-add-member
and add zone for this member by #zone-create-zone.
b) For host api add user and also add zone for this user.
1 During this both options I have problem. When New Users (or member) trying to use “create zone” there is error “Permission denied”.
What should I do more to avoid this?
2 Second problem which I have is that if I am trying to create zone by main user (by api cloudflare) there is error
“code”:1049,“message”:“yourdomain is not a registered domain”. But It is registered.
What should I do more to avoid this?

WRT the 1049, given the zone exists, I suspect the name servers for that domain are not responsive. Here is a good tip on 1049, Community Tip - Fixing Code: 1049 example.com is not a registered domain.

Thank You cloonan for response. That looks reasonable. I will try find problem at domain provider.