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. Please reach out to the person requesting the IAT/ICA number to understand the significance of this number.
Please email email@example.com, if you would like someone to help you find a point of contact that may be able to assist you.
The IAT number is not assigned by Visa. The "iat" (issued at) claim identifies the time at which the JWT was issued. This claim can be used to determine the age of the JWT. Its value MUST be a number containing a NumericDate value. Use of this claim is OPTIONAL. For additional information on IAT please visit this link.https://tools.ietf.org/html/rfc7519
IAT is for the occasional web token and it is for standard industry technology. It is for building a case in the web token. The IAT number, is a number that is assigned by a developer who is generating the token. The IAT number is generated by the developer creating the web token and is industry standard.