Plex and Avalara integration

What moves between them

Plex purchase orders and sales orders flow into Avalara for tax calculation. When a new or modified order arrives in Plex, ml-connector extracts the customer or supplier address, line items, and destination, submits the transaction to Avalara for real-time tax calculation, and writes the computed tax back into Plex so the order is ready for posting. Tax data moves one direction only, from Avalara into Plex, because Avalara is read-only and does not accept write-backs of GL postings.

How ml-connector handles it

ml-connector bridges two separate authentication systems: it holds Plex OAuth 2.0 credentials and refreshes the bearer token when needed, and separately maintains Avalara Account ID and License Key credentials for HTTP Basic Authentication. On a polling cycle configured to your order volume and approval rhythm, it reads modified Plex purchase orders and sales orders, validates the ship-to or bill-to address using Avalara's address resolution endpoint to catch geocoding failures before tax calculation, submits each line to Avalara as a transaction, receives the calculated tax, and upserts the amount into the Plex order document. Avalara returns HTTP 429 when rate limits are exceeded; ml-connector backs off exponentially and retries. Because Avalara uses the document code as an idempotency key, resubmitting the same order code returns the cached result rather than recalculating, so retries are safe and deduplication is automatic.

A real-world example

A mid-market automotive supplier manufactures parts for OEMs and also resells components to smaller shops across five states. Previously, the finance team used Plex for all orders and inventory, but calculated tax manually using state-by-state lookup tables, then hand-entered the amounts into each order before posting to the ledger. This was error-prone and created month-end reconciliation work. With Plex and Avalara connected, every purchase order and sales order is automatically taxed according to the destination state and local jurisdiction the moment the order is finalized in Plex, so the accounting team can post and close the books on time.

What you can do

• •Automatically calculate sales and use tax on Plex purchase orders and sales orders using real-time Avalara tax rates and rules.
• •Validate customer and supplier addresses against Avalara's database before tax calculation to prevent failures and ensure accurate jurisdiction determination.
• •Write computed tax amounts directly into Plex order documents so finance has the correct liability before posting to the general ledger.
• •Authenticate Plex with OAuth 2.0 and Avalara with HTTP Basic Authentication, managing both credential sets encrypted and refreshing tokens when needed.
• •Poll Plex on a configurable interval aligned to your order cadence, with exponential backoff on rate limits and a full audit trail on every transaction.

Questions

Which direction does tax data flow between Plex and Avalara?

Tax data flows from Avalara into Plex only. Plex orders are submitted to Avalara for real-time tax calculation, and the computed tax is written back into the Plex order so it is correct before posting. Avalara does not accept write-backs from Plex, since Avalara's tax calculations are the source of truth for compliance.

How does the integration handle address validation to prevent tax calculation errors?

Before submitting an order to Avalara for tax calculation, ml-connector validates the ship-to or bill-to address using Avalara's /addresses/resolve endpoint. If the address cannot be validated, the integration surfaces the error so the order address can be corrected in Plex before re-attempting tax calculation. This prevents invalid addresses from causing tax failures and ensures the jurisdiction is correctly determined.

What happens if Avalara rate limits are exceeded during bulk order processing?

When Avalara returns HTTP 429, ml-connector backs off exponentially and retries the request. Because Avalara uses the document code as an idempotency key, retrying the same order code returns the cached tax result rather than recalculating, so the integration recovers gracefully without losing data or creating duplicate tax entries.