Region map: Map postcode data to custom GeoJSON URL's regional identifiers

Hi,
From my data I have a column of postcodes along with a column for the amount contributed from a particular postcode. There is also a longitude and latitude columns in my data that specifies the postcodes world map coordinates.
Number of rows of this data can change, as some are added and some removed.

I want to be able to find the total amount contributed for each region on a custom map .
The map is split into different custom regions specified in the GeoJSON file of the map I attached .

The issue is I don't have a way to map the regional identifiers from the GeoJSON file to the Postcodes. So I need a way to identify regions a postcode lies in.

Has anyone done something similar to this in metabase?