there is a limit:
You can create a maximum of 10 Accounts per IP Address per 3 hours. You can create a maximum of 500 Accounts per IP Range within an IPv6 /48 per 3 hours. Hitting either account rate limit is very rare, and we recommend that large integrators prefer a design using one account for many customers.
Looks like you have the wrong design.
You shouldn't create one account per new domain name.
PS: Create one account, then use that account with different domain names + renews. So don't create new accounts automatic.