fix ERROR_CODE encoding

neps/nep-0488.md

@@ -481,13 +481,14 @@ will successfully complete its work but return an ERROR_CODE.
 This enables users to handle error cases independently. It's important to note that host functions
 might terminate with an error if it's straightforward to avoid it (e.g., incorrect input size).
 
-The ERROR_CODE is encoded as a little-endian u64 and can hold the following values:
+The ERROR_CODE is an u64 and can hold the following values:
 
-- 0: No error, execution was successful.
+- 0: No error, execution was successful. For `bls12381_pairing_check` function, the pairing result equals the multiplicative identity.
 - 1: Execution finished with error due to:
   - Incorrect encoding (e.g., incorrectly set compression/decompression bit, coordinate >= p, etc.). 
   - A point not on the curve (where applicable). 
   - A point not in the expected subgroup (where applicable).
+- 2: Can be returned only in `bls12381_pairing_check`. No error, execution was successful, but the pairing result doesn't equal the multiplicative identity. 
 
 #### General comments
 
@@ -916,14 +917,12 @@ We don’t need to calculate the pairing function itself as the result would lie
 
 The ERROR_CODE is returned.
 
-- ERROR_CODE = 0: the input is correct
-  - <ins>Output:</ins> 1 byte with two possible values: 1 if the pairing result equals the multiplicative identity, and 0 otherwise.
+- ERROR_CODE = 0: the input is correct, the pairing result equals the multiplicative identity.
 - ERROR_CODE = 1:
   - Points encoded incorrectly (refer to the Curve Points Encoded section).
   - Point not on the curve.
   - Point not in $G_1/G_2$.
-
-For an empty input, the function returns ERROR_CODE = 0.
+- ERROR_CODE = 2: the input is correct, the pairing result doesn't equal the multiplicative identity.
 
 ***Test cases:***