I am new to Power Automate, so please forgive my ignorance.
I am creating a flow to read in a CSV file and check that all records exist on the Items table, where they don't I want to create a new record

However, I need to set the VAT Prod Posting Group but this field doesn't seem to be available. As it is a standard field I don't understand why I cannot set it?

I have read that I can add this using extensions or custom APIs, but I'm unsure how to progress with this.
Can anyone advise?