I've just upgraded the plan still I can't track the orders, why is it so?

Order Status Tracker provides unlimited order lookups. Once you run out of your plan order limits, the orders outside your quota will no longer be synced. Let us give you an example to clarify any confusion.

Let's assume that I'm a new user and on a free plan of the app. Then my customers will only be able to track the first 25 orders placed in the store ("Not tracked"). 

Once the limit of 25 orders is exceeded (let's say the limit is exceeded on the 10th date of that month), no further order details will be passed to the tracking service until they upgrade the plan. (Let's assume that I've upgraded the plan (on the 15th date of that month) then the order service will be resumed. 

Here, the orders placed between the 10th and 15th date won't be tracked as no details are passed to the Easy post service.