Unable to Patch/update custom property data on the profile with Patch API

Please find the below observation on PATCH API.

When an account is getting updated with membership details in Salesforce we need to update the same in Klaviyo as well. Hence we need to use PATCH API from Klaviyo.

While testing the PATCH API in Postman, we observed that custom properties are not getting updated and if we add new properties(with new names other than existing property name) in the append section of patch properties, then the new properties are getting added in the custom properties section. If we add new properties for the membership details then it will be having duplicate custom properties instead of updating the same property with new value.

Also the unappend function which removes the custom property mentioned in that section is not working as expected. PFA the screenshot below:

Please support on how to update the existing custom properties.

Thanks in advance!