Issues with Threat Intelligence Upload Indicators API (Preview)

Hi,

Due to Threat Intelligence Platforms connector being deprecated, I'm moving on to the new Threat Intelligence Upload Indicators API (Preview). It installed alright, but I'm struggling with getting the logic app to POST to the new URI due to
{"error":{"code":"UploadIndicatorsValidationErrors","message":"Indicators array is required and cannot be empty. ","target":null,"additionalInfo":null}}

Same is happening even when I'm trying to post a sample request from the reference page:
https://learn.microsoft.com/en-us/azure/sentinel/upload-indicators-api#sample-request-body

Has anyone managed to get this to work?

Cheers!
KubaT