Currently, I can only find
{{subscribe_form placeholder="youremail@example.com"}}
In my theme’s code. This subscribe_form is loaded in server-side, which I don’t have access to, as I’m using Ghost Pro.
Is it possible to customize the on success/error someone subscribing?
Hey there @MLFromScratch 
. This can be done with our new members form, which comes with built in error handling:
https://ghost.org/docs/members/signup-signin-forms/
It also comes with the option to listen to error states as well displaying error messages when a form is unable to submit.
Hope this helps!
Maybe you are confusing members and subscribers. I have not activated the members feature, but I do collect e-mails using the subscriber feature in Ghost.
My question was with regards to new subscribers, if it’s possible to add a cookie once someone successfully subscribes?
Edit: Oops, what was subscribers is now members 