Is there provided facility to hold a call on click of button in CSDK.

Hi Prashant,
Thank you fo your question.

Could you clarify, what facility do you need?

On iOS you can hold a call using the holdWithCompletionHandler: method of the CSCall object.

Once call is established from client side there should be a button to hold call. So after pressing hold button what code needs to be write to hold call at client side (at mobile end).

I got this delegate method of CSCallDelegate
- (void)callDidHold:(CSCall *)call

Now I want know what code should I write to hold a call at mobile end.

Simply use the holdWithCompletionHandler method of the CSCall object

- (void) holdWithCompletionHandler: (void(^)(NSError *error)) handler

https://www.devconnectprogram.com/site/global/products_resources/avaya_client_sdk/programming_docs/current/ios/communication/api_refs/interface_c_s_call.html#a0ce3c0c4095334b5417de60676b4ad36

See code sample below
[call holdWithCompletionHandler:^(NSError *error) {
if (error) {
//error
} else {
//call is held
}
}];