Hi michaellim!
Thanks for posting here. Let me assist you with the difference between QuickBooks Online US and QuickBooks Online Singapore.
There are features that are not available in some regions. For example, QuickBooks Online Singapore doesn't have payroll services. You can use our QBO US Test drive so you can explore more what makes the US version different.
With regard to the API, I suggest you reach out to our developers. They'll be able to further assist you with any integration concerns.
I added this link if you need help in setting up your QBO account: Get started with QuickBooks Online.
I'll be here if you need more help with this. Take care!
