@RishavKaaraTech
Hope you are doing well.
The use of the is recommended along the tool as it offers an easy way of exploring the NTAG424 and other smart cards' features.
The error you are getting (0x9140), refers to an invalid key number that has been specified, meaning that the targeted key does not exist. Please consider that there exist five addressable key fields at application level which are numbered from 00h to 04h, please refer to section 8.2.4 of the to get a deeper understanding on the use of each key and make sure the key you are addressing with the sent command exists.
Consider that enabling SDM is only possible for the "StandardData" file No 02h, and the feature can be enabled using the "ChangeFileSettings" command please see section 11.7.1 of the and section 9.3 for further details on SDM. You may also take a look at section 5 of the app note as it describes the procedure that needs to take place in order to be able to change the file settings and personalize the NTAG 424.
This feature (SDM) can also be enabled and tested using the please refer to section 4 of the for further details.
The online key is meant to be used if an online authentication is needed in the application when the device has internet access, however if this is not necessary on the application, a local authentication can take place using the offline key.
Regards,
Eduardo.