Please reach out to the person who is asking you to provide this number to understand the significance of IAT/ICA.
In reference to Visa Direct, please know that we do not use the IAT number for push payments transaction life cycle anywhere. Visa Direct does not use any IAT number for sending or receiving money. Visa Direct transaction takes place based on the 16-digit sender and recipient PAN.
The IAT/ICA number is not directly related to the Visa Developer Portal, therefore, I will not be able to comment directly on how you will get the IAT/ICA number. You can email firstname.lastname@example.org and someone from the team will find a point of contact to reach out to you.
I sent the same request to that email address and waiting reply.
Question is, why someone will ask for this information to make a payment? What will be the reason?