What you're looking for is https://wiki.freeswitch.org/wiki/Variable_instant_ringback
You should add session:execute("set","instant_ringback=true");
just after L392 inside freeswitch/scripts/astpp/lib/astpp.callingcards.function.lua

I haven't tested this but it's (similar) worked for me on other projects.

Thank you, [~dedayoa] dedayoa!

You're welcome @slango-im

[~dedayoa] , just wanted to follow up on this. I added this line of code to the "astpp.callingcards.function.lua" file the instant ringback did not work.

Were you able to make it work on another freeswitch?

Any updates on this - perhaps ASTPP does not support this?

We added session:execute("set","instant_ringback=true"); but it still does not work.

@slango-im If the delay is from DID provider side than call will take time to reach to ASTPP server and no change to dialplan will work if call is not reaching to ASTPP server.

@slango-im
For outgoing calls ringing as soon as you select the gateway it is possible to make the following configuration:

In the Gateway DialPlan Variable:

bypass_media=false,instant_ringback=true,ringback=${us-ring}