If you run a US shipping operation on ERPNext, the last mile is usually a swivel-chair mess. Your Sales Orders and Delivery Notes live in ERPNext, but rating a parcel, buying postage, printing a label, and filling out a customs form all happen on USPS.com or a separate postage tool. Reps re-key addresses and weights, quote shipping from a rate table that went stale months ago, and paste tracking numbers back into ERPNext by hand — when they remember to at all. ERPNext core ships a generic Shipment DocType and a Shipping Rule engine, but it has no USPS carrier integration, no live rate calls, no label generation, and no customs-form output. Native runs out of road the moment you need a real USPS rate or a scannable label.

We build a proper Frappe app — its own module, DocTypes, and hooks.py — installed on your bench, not a brittle pile of copy-pasted scripts. It authenticates to the modern USPS APIs using OAuth2 client-credentials against the Ship/Rates, Addresses, and Tracking endpoints, with credentials held in an encrypted USPS Settings single DocType behind a sandbox/production toggle. From a Delivery Note or Shipment, a whitelisted server method (ecosire_usps.api.get_rates) calls the USPS Rates API and returns live Priority Mail, Priority Mail Express, Ground Advantage, and First-Class/Media Mail options based on the shipment's actual weight, package dimensions, origin ZIP, and destination — so reps quote the real number instead of a guess.

When a rep picks a rate, a second whitelisted method buys the label, stores the returned PDF/ZPL as a File attached to the document, writes the USPS tracking number back onto the Delivery Note, and — for international shipments — generates the correct CN22 or CP72 customs declaration from the item lines (HS codes, country of origin, declared value). Addresses are run through the USPS Addresses API for standardization and ZIP+4 correction before a label is ever bought, so you stop paying for undeliverable-address surcharges. A scheduler event polls the Tracking API on the interval you choose, appends each scan event to a child table on the shipment, and moves the status through In Transit / Delivered / Exception, optionally emailing the customer. Everything is wrapped in role-based permissions and Client Scripts so buttons only appear for the right roles and the workflow feels native to ERPNext.

Because this is build-to-order, nothing ships until we agree on scope. We start with a short scoping call, confirm which USPS services, package profiles, and document types you use, and hand you a fixed statement of work. We build against Frappe/ERPNext v15 or v16 on a staging copy of your site, run UAT with your team, then install on production behind a rollback plan. You receive the full source in a Git repository you own, plus documentation, a training session, and a post-go-live support window — no black boxes, no lock-in.