As I am new to encryption and particularly in Java/Android, I am struggling to find tutorials and code that work fine so that I can learn from them but the results.
As in this site: https://www.owasp.org/index.php/Using_the_Java_Cryptographic_Extensions
I couldn't find the problem that hit me with
The encryption and decryption process worked fine after: I replaced the byte array obtained from :
byte array of message string as instructed in
So even though my problem is not fully solved, this question should be marked as answered.