What the TSS API actually offers
The Trader Support Service exposes an API that allows authorised customs agents to submit declarations programmatically instead of through the portal. For freight forwarders with repeat-lane volume, this is where scaling stops meaning more people and starts meaning cleaner pipelines.
Prerequisites
You need an agent account (converted from trader, one-way), individual client authorisations, MFA-capable service accounts, and source data clean enough to survive schema validation without hand-repair.
Watch the 99-item limit
A single TSS declaration is capped at 99 items. Consolidated loads exceeding that must be split before submission. This TSS software for freight forwarders guide covers the splitting decision as part of the portal-vs-API choice.
Client-scoped identifiers
Every declaration must carry the correct client EORI and, where relevant, the client UKIMS authorisation. Hard-coding these into shared config is where multi-client integrations most often fail.
Exception handling in code
The API returns rejections and amendments that must be routed back to the right client. Design your exception queue with the client context attached, not the submission ID alone.
When API is the wrong answer
Ad-hoc consolidated loads, low-volume clients, and new movement types often submit faster through the portal. Automation earns its keep on repeat shapes.
See a multi-client TSS integration in production. Watch a demo.
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