I have a MacOS 10.13.6, I just purchase Microsoft package but can't install on my Mac.

Hello. To start, what "Microsoft Package" did you purchase for installation on your Mac? Did you purchase Microsoft Office? If so, what version? Depending on the version of Microsoft Office you purchased, it may no longer support macOS 10.13. Microsoft states that Office 2021 for Mac is supported on the three most recent versions of macOS, meaning that macOS 10.13 High Sierra is no longer supported.

You may be able to upgrade to a newer version of macOS, such as macOS Catalina, but this is dependent on the age of your Mac. macOS Catalina is compatible with these computers.

Hello. It looks like Microsoft Office 16.54 is the latest version available. As such, it only supports the three most recent versions of macOS. With macOS Monterey now released, this means that only Monterey, Big Sur, and Catalina are supported by Microsoft. Your version of macOS, High Sierra, is no longer supported.

If your computer is unable to upgrade to macOS Catalina, then your best option is to request a refund for this software. You will need to reach out to Microsoft or the seller your purchased the product from in order to accomplish this.

MacPro2021 wrote:

I have purchased Microsoft_Office_16.54.21101001_HomeStudent package. Is there a way that I can install this on MacOS 10.13?

No

If not, can I get reimbursed for the purchase?

Ask whoever you bought it from.