The GitHub sample is referencing to this public OpenAI doc URL: https://platform.openai.com/docs/api-reference/introduction - for "Learn how to switch to OpenAI instance".
I have a raised an issue on the GitHub directly for author to fix :
You may track it here: https://github.com/Azure-Samples/azure-search-openai-demo/issues/1039
For your reference, also please check these docs:
Get up and running with the OpenAI API
Open AI | api-reference?lang=python
I understand you have mentioned about the right email prerequisite, just to highlight, you need to receive confirmation that your subscription for the Open AI service was enabled after submitting the registration form.
As for the error message: The subscription does not have QuotaId/Feature required by SKU 'S0' from kind 'OpenAI' or contains blocked QuotaId/Feature - Just to highlight, you have to chose the right region for deployment in the script that was approved (location that you selected' in the registration form). For example: As kylgrn mentioned ensure that you are not attempting to provision in EastUS2 when you chose EastUS in the form.
Ref: Limited access to Azure OpenAI Service and GitHub discussion