There are a couple of reasons why you may be asked to purchase postage.
You do not have enough postage in your Endicia account.
In order to purchase USPS postage, you will need to maintain a postage balance in your Endicia account. Learn more.
You have the exact amount of postage you need for your current purchase.
Endicia does not permit a zero dollar balance on an active account. If you have just enough postage to cover the label purchase but you're still receiving the notification, you'll need to add postage to continue. We typically recommend leaving even just a few dollars in your account so you don't run into this situation. Learn more.
If you are concerned about this happening and halting your shipping process, we recommend looking at how you can set up automatic refills on your account. Learn how to set up automatic postage refills.