I need to pass this encrypted value in JMeter & every time there will be a similar kind of unique encryption passing. yS0TNeqqu9py3NogSvUN6JJMC0on34ezkU2BQkpSR59gMelrTL+B1kds0ggNjmPvBNBJ6QCz94aG0B1pu1qyLslClzsyZUP2j1OXX3vTka+s6iTIE7Kp3bkF3oMwMX+dXSQx7AmQYc90h6v3DMEDa1uM0w/aun5Ap9uoPHGHh8FniHvvpC6w6xYKDptQ2xc+MlcYZLWNBqSFY0hWwnsVSpcRqu11q3RaxR4l9QcO/vDjRwVJYREBPCGe1Ep4vRt5Rl//+nHZ1IzRRSXcVmwkUo1Mfoirw5YvxbhoGGntiVqKUsDiipVMKxZYZBGLJWGQcAtIAQkv33VJPwgz0gba+Q==
I tried with ${__base64Encode()} but its not working.
You need to determine encryption algorithm like AES or RSA which is being used for encoding and implement the same using JSR223 PreProcessor and Groovy language.
You can inspect your page JavaScript code and look for the function which performs the password encryption, you should be able to guess the algorithm and its parameters from there.
More information: Encryption and decryption with Groovy