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FeaturesagentOS Direct DebitUpdated March 13, 2026

Stronger Bank Detail Validation on the Mandate Form

Stronger Bank Detail Validation on the Mandate Form

Released in v1.0.30

Overview

v1.0.30 introduces rigorous validation of UK sort codes and account numbers on the tenant-facing mandate form. Validation runs both in the browser as the tenant fills in their details, and again on the server before the mandate is submitted to Modulr for AUDDIS registration. This catches invalid combinations early and avoids unnecessary failed mandate registrations in the BACS cycle.

How Validation Works

1. Modulus Check

Every sort code and account number combination is run through a UK modulus check using a dedicated validation library. The modulus check applies the standard UK banking validation rules (Vocalink modulus checking specification) to confirm the combination is arithmetically valid.

  • If the combination fails the modulus check, the tenant sees an error immediately and cannot proceed.
  • This check runs client-side on blur/change and is repeated server-side on form submission.

2. Sort Code Lookup

When a tenant enters a sort code, the service looks it up against a UK sort code directory to:

  • Display the bank name — the matched bank name is shown beneath the sort code field so the tenant can confirm they have entered the correct code.
  • Verify Direct Debit support — not all sort codes support Direct Debit (e.g. some building society roll number accounts, some business-only sort codes). If the sort code does not support DD, the tenant is informed and cannot continue with those details.

3. Account Holder Name Matching

The account holder name entered by the tenant is matched against the name associated with the provided sort code and account number. A mismatch surfaces a warning (or hard error, depending on configuration) to prevent mandates being registered against accounts the tenant does not control.

Why This Matters

BACS mandate registration (AUDDIS) operates on a fixed processing cycle. A failed submission — caused by an invalid sort code, an unsupported account type, or a name mismatch — means the mandate cannot be activated until the next available processing window, delaying rent collection by days. By catching these errors at the point of data entry, v1.0.30 removes the most common cause of first-attempt AUDDIS failures.

Tenant Experience

  • Errors appear inline beneath the relevant field as soon as the tenant moves focus away from it.
  • The bank name is displayed automatically after a valid sort code is entered — no extra action required from the tenant.
  • Error messages are plain-language and actionable (e.g. "This sort code does not support Direct Debit. Please check your details or contact your bank.").

No API Changes

This release does not change the mandate API contract. Validation is enforced at the form layer and internally before AUDDIS submission. Existing integrations are unaffected.