An ERP that raises GST documents has to treat the e-invoice and e-way bill portals as steps in billing and despatch, not as an afterthought. The invoice is not complete until the portal returns an Invoice Reference Number (IRN), and a truck should not leave without a valid e-way bill. Most integration failures come from five places: the IRN that blocks the invoice, the cancellation window, vehicle details after despatch, validity and extension, and reconciliation.
This article describes engineering concerns. It is not tax advice. Confirm current rules and thresholds on the official portals and with your tax adviser.
Which rules apply
Rules change, so each figure below is attributed to its source.
- E-invoice threshold. As reported by TaxGuru (October 2026), e-invoicing applies under Notification No. 10/2023-Central Tax of 10 May 2023, which set the turnover limit that applies from 1 August 2023 (the linked report gives the amount). The e-invoice portal's own page, Crossed the e-invoicing turnover limit?, explains what to do next.
- 30-day reporting. As reported by Business Today, citing a GSTN advisory dated 5 November 2024, taxpayers above the aggregate-turnover limit named in the advisory cannot report an invoice to the e-invoice portal more than 30 days after its date, from 1 April 2025.
- E-way bill value threshold and validity. As summarised by Tally Solutions, the standard value threshold applies to inter-state movement (the linked page gives the amount), validity is one day for the first 200 km and one more day for each further 200 km or part, and validity can be extended within 8 hours before or after expiry. Intra-state limits vary by state.
- E-invoice cancellation. The e-invoice portal's knowledge base states that an IRN can be cancelled within 24 hours of submitting the invoice. See the IRN cancellation page.
Where integrations break
The IRN blocks the invoice
The portal, called the Invoice Registration Portal or IRP, signs the invoice and returns the IRN and a QR code. Until then, the invoice is not in its final form. If the ERP posts the invoice first and calls the portal later, a portal outage leaves posted invoices with no IRN, and dispatch stops. Decide the order on purpose: either call the portal before the invoice is final, or keep a clear "awaiting IRN" status that blocks printing and despatch.
The 24-hour cancellation window
According to the portal page above, once an IRN is cancelled the same invoice number cannot be used to generate another, and when an e-way bill exists it has to be cancelled first. After the window, the supplier issues a credit or debit note, or corrects the details in the GSTR-1 return. The ERP should warn users when a cancel request is about to miss the window, and should make "cancel the e-way bill first" a built-in step.
Vehicle details after the truck leaves
Each e-way bill is split in two. Part A carries the consignment details; Part B carries the vehicle or transport document number. Plans change at the gate: a vehicle breaks down, a load is transferred, a transporter swaps a truck. The ERP needs a quick way for the despatch desk or transporter to update Part B, and it should show who changed it and when.
Validity, distance and journeys with several legs
Validity depends on distance, and journeys can have several legs. The ERP should compute the expiry time when the bill is created, show it to the despatch desk, and prompt for an extension before it lapses. Per the Tally summary above, the extension window is eight hours either side of expiry, so set the alert for the moment that window opens, 8 hours before expiry, which leaves the whole window to act.
Reconciliation is skipped
Three records should agree: the ERP invoice, the IRN data on the portal and the outward-supplies return (GSTR-1). Differences arise from late cancellations, manual corrections on the portal and failed calls. Run a daily comparison, and list every invoice that has no IRN or no e-way bill when it should.
Five design rules
- Asynchronous, with retries. Send portal calls through a queue, retry with increasing delays, and show the user a status instead of a spinner.
- Idempotency on every call. If a request times out, the ERP must be able to ask whether the document was created before it sends a second request. Otherwise, a retry can create a duplicate or a rejection.
- Store the full response. Keep the IRN, acknowledgement number and date, the signed invoice, the QR payload and any error codes with the invoice record.
- Make the clock visible. Show cancellation deadlines, e-way bill expiry and the 30-day reporting limit as a dated field on screen, not as a rule in a manual.
- Fail at the gate. Block despatch for an invoice that lacks a required IRN or e-way bill, at the gate pass or loading step. An error in a log file helps nobody at 11 p.m.
Direct connection or a provider
Companies reach the portals in two ways: through an authorised provider that hosts the connection, or by connecting to the portal directly. A provider shortens set-up, and a direct link gives more control and fewer parties in the path. Check the current onboarding and eligibility rules on the portal before you decide. Either way, keep your integration code behind one internal interface so that you can change route without touching billing logic.
Why this belongs inside the ERP
A separate portal session means a second data entry for each despatch, and a second place where the two records can disagree. In an ERP that handles it as part of order-to-despatch, the invoice, the IRN, the e-way bill and the gate pass share one record. The steel manufacturer ERP case study describes dispatch with e-way integration built into the flow. For the wider cost picture, see the five cost drivers of a custom ERP. For the party and item fields the portals require, see moving data into a new ERP.
Questions buyers ask
Does the ERP need the e-invoice portal to issue every invoice?
For businesses above the threshold, the portal returns the IRN that completes the invoice, so the ERP must call it as part of billing.
What happens if the portal is down?
Use a queue and an "awaiting IRN" status, so billing continues and documents are completed when the portal returns.
Can an IRN be corrected?
Within the cancellation window it can be cancelled. After that, use a credit or debit note, or correct the return, as the portal page above describes.
Where Brihat Infotech fits
Brihat Infotech connects ERPs to the GST e-invoice and e-way bill portals as part of its systems integration and API work and its custom ERP builds. Start a conversation.