To search for emails with Reply Chrome Extension, each new user gets 200 emails per month included in the subscription. It is also possible to switch to unlimited emails for 49$ per month.
Once you use 75%/90% of your monthly limit or exceed it, you get a notification to upgrade your subscription. To check the number of searches used for the current month/upgrade it to an unlimited number of emails:
Go to the Settings page -> Plans & Billing tab -> Subscription section.
NOTE: It is important that you have a valid Reply account to use the Reply Chrome Extension.