Sub customers created via API do not convert to Projects, they say "Converted" but don't convert. This happens with multiple accounts.

Welcome to the Community space, Snapfroz. I'll point you in the right direction to help you fix this and convert sub customers to projects inside QuickBooks Online (QBO).

Before we proceed, can you tell us more about the live accounts where you encountered the issue? We have a separate forum where you can interact with the developers, product experts, and engineers about software, QuickBooks API concerns, Product integration, or developer license-related questions. That said, we recommend posting this question to our Intuit Developer Community. They have the tools and resources available to assist you in resolving your concerns. These are the steps:

1. In your browser, type this link: https://help.developer.intuit.com/s/
2. Choose your QuickBooks product.
3. Click the Ask a Question button.
4. Press Sign In.
5. Enter your Intuit login credentials.

In addition, here's an article to help you manage projects and keep track of its profitability: Create and manage projects in QuickBooks Online.

You can always comment below if you have any additional QuickBooks-related concerns or need assistance with customers or project-related tasks. Rest assured, Our team will be around to help you out again. Keep safe.