Relation, authorisation and sequence errorsExternal validation

CDS12134DUCR and MUCR formats not valid

HMRC explanation

MUCR or DUCR format is not valid
If the MUCR was given to you, check it is in a valid format. If you created it yourself, check the guidance on the correct format (opens in new tab).
If you have declared a previous declaration reference such as for an import, check the DUCR on the previous declaration.

Source: HMRC, Customs Declaration Service error codes, Open Government Licence v3.0. GOV.UK publication · Licence

What to check across the Relation, authorisation and sequence errors

Two elements, or a value and a rule, disagree. Read both elements together: completing one element with a particular code often requires another value, and the fault is frequently in the element you did not change. The family also covers parties and authorisations that are not recognised, references that must be unique, and messages sent out of sequence.

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Source: HMRC, Customs Declaration Service error codes, Open Government Licence v3.0. GOV.UK publication · Licence