Duplicate domain error with aggregator account for creating a store for partner site

We operate with partner stores that grant us permission to promote their products on Microsoft Shopping. However, the support we have received from Microsoft is unproductive. Despite several months of effort, we have been unable to create a single store through the API. I will outline the issues we encountered during the process:

1. Initially, when attempting to create a store through the API, we encountered an error related to using a non-Microsoft verified domain. The support team advised us to use a Microsoft verified domain, which we promptly did.
2. Subsequently, we faced another error, and the support team informed us that our account should be an Aggregator account. We agreed and requested them to make the necessary changes.
3. However, upon trying again, we encountered a duplicate domain error, hindering our progress.

This leads to the following questions and concerns:

• If Microsoft does not allow the use of domains for new stores(who might have store from the owner), how are we expected to create a store?
• What is the purpose of an Aggregator Account if domain stores can only be created in a single account?Like suppose if the owner create a store in his own account the aggregator won't be able to create for them and eventually wouldn't be able to promote
• We have noticed that importing stores from Google Ads/Google Merchant Center is supported. If that is the case, why is it not possible to create the same store using API?
• If our approach is entirely wrong, and creating stores through the API is not feasible, we urgently need a solution. With over 10000 partner stores and a vast inventory of over 60M products, we need to find a way to promote them through individual campaigns in different countries using Microsoft Ads and want to automate the process using API.

We have been seeking assistance from Microsoft support for over 5 months now, with no tangible results. We are reaching out for any helpful guidance or support from anyone who can offer a solution.

It is also be noted that We are Google CSS premium partners and we do the same thing there

Thank you for your consideration.