Fetch Monthly advertising billing invoices using API

I am writing to request your assistance in fetching invoices from Microsoft Advertising using the API. Despite having reviewed the available documentation, I am experiencing challenges in successfully implementing the API calls to retrieve invoice data. I would greatly appreciate your guidance on the following:

Prerequisite Steps: I need a detailed step-by-step process to set up the necessary environment and obtain the appropriate permissions to access invoice data via the Microsoft Advertising API. Additionally, please confirm if there are any specific roles or permissions required for API access.

API Access and Authentication: I require assistance with the authentication process using OAuth2 to obtain access tokens. If there are any common pitfalls or specific configurations needed for Microsoft Advertising, please share those insights.

Sample Code for Proof of Concept: I would appreciate it if you could provide a basic sample code snippet in C# (or another suitable programming language) that demonstrates the correct implementation of API calls to fetch invoices. This will assist me in developing a proof of concept and ensuring that my API interactions are correctly structured.

Additional Resources or Documentation: If there are any additional resources, such as articles, tutorials, or FAQs, that could aid in understanding the integration better, please point me toward them.

Thank you for your time and assistance. I look forward to your prompt response to help resolve these queries.