I was using a simple subscription button in paypal for my clients. But Now, I want to use the Smart subscribe button. I figured out the code and subscriptions. But I am worrying about adding client’s store information as custom details with paypal response from webhook.

I found that there is a custom_id param that can be used to get custom details, I have passed in the subscribe button short code. But I also found that it is used for Invoice Id or subscriber Id. (I checked reply here >> https://www.paypal-community.com/t5/SDKs/showing-custom-id-information-in-a-subscription/td-p/3032291)
So I am confused about whether it is feasible to use for sending extra information with a subscription response in form of custom_id ?

I also want to confirm that I can use IPN response with a smart subscribe button ? Because I can not have a custom field in IPN response from Smart subscribe button, How can I get passed custom information to my IPN file?

Any guidance regarding my issue will be helpful.
Thanks in advance for your time.