Current daily and monthly legal and financial limits on debit and credit cards impacts us negatively during high volume periods, and Stamps.com has an ACH funding capability that could likely be integrated into ShipStation somehow.
We don't need to add anything to the integration for this, actually! Please contact ShipStation support if you'd like to request your postage purchase limit be raised.
The default limit on a balance for Stamps accounts connected to ShipStation is $500. You can request to raise that limit up to $2500. Our team can make the account adjustment to the Stamps account so ShipStation will not block a purchase that puts your balance over the $500 default.