Your system submits an invoice to MyInvois, and instead of a clean validation you get back a rejection—often with a terse error code and not much explanation. Now the document isn't valid, the customer can't rely on it, and someone has to figure out what went wrong before the clock runs out.

After helping businesses debug their MyInvois submissions, I've found that the same handful of errors account for the overwhelming majority of rejections. Here's what they mean and how to fix them—so you can resolve issues quickly instead of guessing.

First: Understand What 'Rejected' Actually Means

MyInvois validation has a few distinct outcomes, and confusing them leads to wasted effort:

• Invalid — the document failed LHDN's validation rules (structure, signature, or data). It was not accepted and must be corrected and resubmitted.
• Rejected by buyer — the document was valid, but the buyer requested rejection within the allowed window (e.g. wrong details). The seller must cancel and reissue.
• Submission failure — the request never got far enough to validate, usually an authentication, formatting, or connectivity problem.

Knowing which bucket you're in tells you where to look—your data, your signing, or your connection.

The Most Common Validation Errors

1. Invalid or Mismatched TIN

By far the most frequent issue. The Tax Identification Number you submitted doesn't validate against LHDN's records, or the TIN doesn't match the associated registration details. This happens with both supplier and buyer TINs.

Fix: Verify the TIN through LHDN's validation before submission, not after. Clean your customer master data so TINs are stored in the correct format. For B2B, confirm the buyer's TIN with them directly rather than guessing.

2. Digital Signature Validation Failure

The document's digital signature couldn't be verified. Causes include an expired or invalid certificate, incorrect canonicalization, a wrong hashing step, or the signed content not matching the submitted content.

Fix: Confirm your digital certificate is valid and not expired. Re-check your XAdES signing implementation against the spec—signature failures are almost always an implementation detail, not a data issue. This is the error most worth getting expert eyes on.

3. Missing or Invalid Classification Code

Every line item needs a valid classification code, and the codes must come from LHDN's accepted list. A missing, outdated, or mistyped code fails validation.

Fix: Map your products and services to the correct classification codes once, store them properly, and validate against the current code list. Don't hardcode a single 'catch-all' code—that can itself cause rejections or compliance issues.

4. Tax Type / Tax Amount Inconsistencies

The declared tax type, rate, or computed tax amount doesn't reconcile with the line totals and invoice total. Rounding differences and incorrect tax treatment are common culprits.

Fix: Ensure your tax calculation and rounding logic matches LHDN's expectations exactly. The totals must add up to the cent. Legacy systems with their own rounding quirks often need this logic adjusted specifically for e-invoice submission.

5. Required Field Missing or Wrong Type

A mandatory field is empty, or a value is the wrong data type or format (for example, a date in the wrong format, or a number sent as text). The UBL/JSON schema is strict.

Fix: Validate your document against LHDN's schema before sending. Build a pre-submission check that catches missing required fields and format errors—cheaper than a round-trip rejection.

6. Duplicate Submission

The same invoice (same document number) was submitted more than once. Often caused by a retry that didn't check whether the first attempt actually succeeded.

Fix: Make submissions idempotent—track each document's status so retries don't resubmit something already accepted. This ties directly into handling asynchronous validation properly.

Why Legacy Systems Hit These Errors More Often

If your invoices keep getting rejected, the root cause is frequently not the e-invoice integration itself but the data and logic feeding it:

• Customer records with missing, malformed, or outdated TINs accumulated over years.
• Product catalogues with no concept of LHDN classification codes.
• Tax and rounding logic written for printed invoices, not for cent-exact API validation.
• No pre-submission validation layer, so bad data only fails once it reaches LHDN.
• Retry logic that resubmits blindly, creating duplicates.

A Practical Troubleshooting Checklist

1. Identify the outcome type: Invalid, buyer-rejected, or submission failure.
2. Read the specific error code and field reference LHDN returned—don't guess.
3. If it's a signature error, treat it as an implementation issue and verify your certificate and signing steps.
4. If it's a data error (TIN, classification, totals), fix the source record, not just this one document.
5. Add a pre-submission check so the same class of error can't reach LHDN again.
6. Confirm the corrected document validates in sandbox before resubmitting to production.
7. Respect the cancellation and rejection windows—use credit/debit notes when the window has passed.

Rejections are frustrating, but they're rarely random. Almost every one traces back to a specific, fixable cause—and once you've built proper validation and signing, the rejection rate drops close to zero.