Expression "replace" not working

Friends in my test project I wanted to try to encrypt text data using a "replace" statement.

You write the text and press the "Submit" button.

The text appears in the "text" plugin.

Then when we click on the "Decrypt" button, the text from the text plugin goes to our other plugin "textbox" and it should decrypt the data from there.

Now I'll tell you how I did it.

You write let's say the letter "a" and it converts it to random characters and numbers. Here is an example of encryption.

replace(Ciphertext.Text,"a","{${½g8w09eg64")

And here is an example of decryption. It's just the reverse side of the encryption, I swapped the letter "a" and "{${½g8w09eg64"

replace(Ciphertext.Text,"{${½g8w09eg64","a")

Encryption works but decryption doesn't work.

Here are the screenshots