External validation errorsExternal validation
CDS50031Request has been received after a successful RET
HMRC explanation
What to check across the External validation errors
A check made outside CDS has not been satisfied: a release response from another system, the format or position of a consignment reference (DUCR or MUCR), an arrival time, or the status of the declaration itself. Check the external reference or status the code names.
A declaration that clears CDS can still be wrong
The free eligibility checker confirms your import activity and whether a free post-clearance audit applies. No data upload, no commitment.
Source: HMRC, Customs Declaration Service error codes, Open Government Licence v3.0. GOV.UK publication · Licence