Finance teams that sell on EMI or installment terms quickly hit the edges of ERPNext core. Native ERPNext gives you a single-value Payment Schedule child table on the Sales Invoice, driven by Payment Terms Template, but it has no concept of a reusable installment product, no automatic interest or profit accrual, no late-fee assessment, and no customer-facing installment statement. Teams end up tracking down-payments, monthly due dates, and overdue penalties in spreadsheets, then manually reconciling them against Payment Entry records — a process that breaks the moment volumes grow or an auditor asks how a balance was derived.

ECOSIRE builds a dedicated Frappe app (its own module, DocTypes, and hooks.py) that turns installment selling into a first-class workflow inside ERPNext. At the center is an Installment Plan Template DocType (number of installments, cadence, down-payment percentage, interest/profit method, grace period, late-fee rule) that finance defines once and applies to a Sales Order or Sales Invoice. On submit, a doc_events hook generates an Installment Schedule — a parent DocType with an Installment Line child table holding each due date, principal, interest, and running balance. A Payment Entry on_submit hook allocates receipts against the correct installment lines, updates their status (Pending, Partially Paid, Paid, Overdue), and recomputes the outstanding balance so the customer ledger and the installment view never drift apart.

The technical build is careful to stay upgrade-safe. Rather than patching core DocTypes, we extend them with Custom Fields and Property Setters delivered via fixtures, and we attach behavior through server scripts and doc_events (validate, on_submit, on_cancel) plus targeted client scripts for the in-form installment preview. A daily scheduler_events job scans open schedules, flags lines past their due date as Overdue, and — where your policy allows — raises the configured late fee as a linked charge. Whitelisted methods (@frappe.whitelist()) expose the schedule and statement over the Frappe REST API so a customer portal, WhatsApp reminder, or external app can read installment status without direct DB access. Role profiles and DocType permissions keep plan creation, fee waivers, and statement generation separated by responsibility.

Because this is build-to-order, nothing ships blind. We start with a short scoping call to confirm your interest/profit method (flat, reducing-balance, or zero-interest EMI), your late-fee policy, tax treatment, and which documents (Sales Order, Sales Invoice, or both) drive the plan. We then build against your Frappe/ERPNext version (v15 or v16), demonstrate on a staging bench, run UAT with your finance team, and install to production with a documented rollback. You receive the full app source and git repository — no black box, no per-seat lock-in. Typical delivery is one working week from confirmed scope.