That's a tricky question. Strictly speaking, it's not recommended. But it's not really recommended to create contacts without an email either; there are always some use cases where it's fine to work around those recommendations. I'd be careful to make sure that you're remaining within the API limits detailed below, but other than that it's fine to use the single 'Create a contact' endpoint in lieu of the batch endpoint.
The batch create/update API requires an email address. While it's not recommended, you can create contacts without an email address using the single 'Create a contact' endpoint:
Thanks for your response, actually I've seen this endpoint but is it recommended to call this url a hundred of times (instead of using the batch api) ?