How To Fix SY421 - Specified comparison operator is not permitted

SY421 - Overview

• Message type: E = Error

• Message class: SY - ABAP/4 system messages

• Message number: 421

• Message text: Specified comparison operator is not permitted

What causes this issue?

You may only use one of the following comparison operators with
conditional watchpoints:

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

>, >=, =, <>, <, >=
The operator that you used here is not allowed.

System Response

How to fix this error?

Use one of the above comparison operators instead.
If you do not use a comparison operator, the debugger will stop
whenever the value changes.

Error message extract from SAP system. Copyright SAP SE.

SY421 - Details

• The SAP error message SY421 ("Specified comparison operator is not permitted") typically occurs in ABAP programming when there is an issue with the use of comparison operators in a conditional statement. This error indicates that the operator used in the comparison is not valid or not allowed in the context where it is being used.
  Causes:
  
  Invalid Operator: The comparison operator used (e.g., =, <>, <, >, <=, >=) is not valid for the data types being compared.
  Data Type Mismatch: The operands being compared may not be compatible data types. For example, comparing a string with a numeric value.
  Syntax Error: There may be a syntax error in the conditional statement that leads to the use of an invalid operator.
  Logical Errors: Using operators in a way that does not make sense logically, such as trying to compare a table with a single value.
  
  Solutions:
  
  Check Operators: Ensure that the comparison operators used are valid for