Error in dynamic action: Value assignment failed (key &1)

What causes this issue?

Key &V1& of conditional check "&V2&" is unknown.
The error can be found in key &V3& of the dynamic actions table.

System Response

The dynamic action was either not run or only partially run or was run
incorrectly.

How to fix this error?

Correct the settings for dynamic actions (table T588Z).
Possible causes of the error:
The constants in conditional checks must be enclosed in inverted commas
(<ZH>'</>const<ZH>'</>), which was not the case.
The field you selected is not available when the dynamic action is run.

Error message extract from SAP system. Copyright SAP SE.