Hello,
We are using JTAPI library 8.1.3, and we need to show different ANI to customer for outbound call.
We have set the value to y for following property.

(SA8481) - Replace Calling Party Number with ASAI ANI? y

Also, while making an outbound call, we are writing *!NUMBER_TO_BE_SHOWN into UUI. But still it is not working.
Is there any other configuration to be done?

What form of trunking is the call egressing over?
See this FAQ for some specific guidance.
https://www.devconnectprogram.com/site/global/products_resources/avaya_aura_application_enablement_services/support/faq/tsapi/index.gsp#790

What AES and CM release are you working with?

It is considerably more complex than just setting number to be shown in the UUI field. Please take a look at this forum thread
https://www.devconnectprogram.com/forums/posts/list/21965.page

or any one of a number of others for comments by Martin Flynn related to this topic.