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. Can you please let me know what company you work for and the Visa APIs that you are interested in using for you business project? Also, please explain what you are referring to when you say, "ISA."
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.
For information on VisaNet, please navigate to the link below.