Sage 300 and Avalara integration

What moves between them

The main flow runs from Sage 300 into Avalara. When an AR invoice or PO is posted in Sage 300, ml-connector polls and detects the new document, formats it for Avalara's transaction schema, and sends it to Avalara for tax calculation. Avalara returns the calculated tax by line and by jurisdiction. ml-connector then writes the tax amounts back into Sage 300 as GL Journal Batch entries allocated to the correct GL accounts and as line-level tax details on the original invoices. This flow runs on a schedule you control, typically tied to your daily AR/AP posting cycle.

How ml-connector handles it

ml-connector stores the HTTP Basic Auth credentials for both systems encrypted at rest. Sage 300 uses uppercase username and password, both of which must be uppercase in the HTTP Basic Auth header; ml-connector enforces this transformation automatically. Avalara uses either Account ID with License Key or Username with Password; ml-connector stores whichever pair you provide. Since both systems support only polling, ml-connector polls Sage 300 ARInvoiceBatches and APInvoiceBatches on a schedule, detects new or updated invoices via date filters, extracts line-item amounts and GL account mappings, and transforms them into Avalara's transaction format. Avalara returns calculated tax as both line-level tax and a summary GL impact. ml-connector maps this back to Sage 300's GL chart of accounts and creates corresponding GLJournalBatches for posting. If Avalara returns 429 Rate Limit errors, ml-connector backs off and retries. Sage 300's IIS server can timeout on high-volume polls (1500+ calls), so ml-connector caps burst rates and spaces requests. Every invoice and tax calculation is logged in full, with the source document code and Avalara transaction ID cross-linked for audit and replay.

A real-world example

A regional specialty retailer with 20 locations uses Sage 300 for invoicing and accounting, and currently estimates sales tax by county and hand-enters tax totals into the general ledger at month-end close. With Sage 300 and Avalara connected, each daily AR invoice is automatically sent to Avalara for real-time multi-jurisdiction tax calculation. The calculated tax posts into Sage 300's GL the same day, mapped to the correct tax payable accounts by state and county. At month-end close, the sales tax accounts are already accurate and reconciled to Avalara, eliminating the manual estimation step and the week-long variance investigation.

What you can do

• •Sync AR and AP invoices from Sage 300 to Avalara for real-time sales and use tax calculation across all jurisdictions.
• •Post calculated tax amounts from Avalara back into Sage 300 as GL Journal Batch entries, allocated to the correct tax accounts by state and jurisdiction.
• •Authenticate Sage 300 with uppercase HTTP Basic Auth and Avalara with Account ID plus License Key, each stored encrypted and secure.
• •Poll Sage 300 and Avalara on a schedule you define, using OData filters to detect only new or updated documents since the last sync.
• •Maintain a full audit trail of every invoice, tax calculation, and GL entry, with source document codes and transaction IDs linked for reconciliation and replay.

Questions

Which direction does data move between Sage 300 and Avalara?

The main flow is Sage 300 into Avalara. Invoices from Sage 300 flow to Avalara for tax calculation. The calculated tax amounts then flow back from Avalara into Sage 300 as GL Journal Batch entries and invoice line-item tax details. Avalara transactions are read-only, so ml-connector never writes tax changes back into Avalara.

Do both Sage 300 usernames and passwords need to be uppercase?

Yes. Sage 300 requires both the username and password to be uppercase in the HTTP Basic Auth header. ml-connector automatically converts credentials to uppercase before encoding them, so you can enter them in any case and the integration handles the transformation correctly.

How does the integration handle Avalara's lack of webhooks?

Both Sage 300 and Avalara support only pull-based polling with no push webhooks. ml-connector polls Sage 300 for new invoices using OData date filters, polls Avalara for the corresponding calculated tax transactions, and runs this cycle on a schedule you define tied to your daily posting cycle. Every poll uses idempotency keys (Sage 300 document IDs and Avalara transaction codes) to ensure no duplicates.