Authorize.Net v/s Authorize.CIM
The main difference between Authorize.net and Authorize.cim regarding payplans is that Authorize.net processes the payment notification once a day. So, you need to wait and check whether subscription gets activated or not in a day.
While in authorizecim, we get instant payment notifications regarding payment.
So, if you have a recurring subscription, then it would be better to use Authorize.cim in order to get instant notification, or if you still want to use Authorize.net, then set Wait for Payment before Expiring Subscription. You will find the Wait for Payment before Expiring Subscription option in the PayPlans > Settings > System.