How do I map a descriptive flexfield value to a custom field object created in Subscription Management?

You can map a descriptive flexfield (DFF) value to a custom field object using one of the following REST API commands on an external web service:

GET <hostname>/fscmRestApi/resources/11.13.18.05/itemsV2/{itemsV2UniqID}/child/ItemDFF

GET <hostname>/fscmRestApi/resources/11.13.18.05/itemsV2/{itemsV2UniqID}/child/ItemDFF/{ItemDFFUniqID}

You must identify the exact value that you provide as {itemsV2UniqID}. Usually this is the InventoryItemId. You must also verify {ItemDFFUniqID}. You can get this from the DFF setup - usually it's the DFF API name.

It's recommended that you test these requests in the Postman sandbox to see what values need to be passed and how exactly they can be retrieved.

After you confirm the tested requests, register the external web service in Application Composer and use a Subscription Management trigger to populate the field you want.