Stamps.com and Express 1 have limits on how much postage your account can contain at a given time, as well as how much you can purchase at once.
Typically, new Stamps.com accounts are limited to $500 in postage at any given time. The maximum purchase is also $500, and the minimum postage purchase is $10.
If you fund your Stamps.com account directly from your bank account (ACH) you may request with Stamps.com directly to increase your postage balance limit. To begin this process, contact Stamps.com Customer Care at 1-888-434-0055 between the hours of 6am and 6pm Pacific Time (9am and 9pm Eastern).
For Express 1, there is a postage purchase limit of $2,500 and a minimum purchase amount of $25.
Please note, we cannot change the default postage purchase that is prompted when you are shipping orders and do not have sufficient balance to cover the postage fees.
However you can purchase a larger amount by adjusting Add Additional Funds value manually on the Ship Order screen, or at any time from the Carriers & Fulfillment page.
To purchase postage from the Carriers & Fulfillment page.
Head to your Account Settings (the wrench icon in the upper right).
Next, select Shipping and then Carriers & Fulfillment from the sidebar on the left.
From here, you can select the Add Funds link for Stamps.com:
or Express 1: