Relation, authorisation and sequence errorsRelation & missing element
CDS12106Relation error: Appropriate Additional Information Code must be provided in DE2/2 with Additional Procedure Code 1CL
HMRC explanation
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