unable to resolve class com...

Dear all,

I'm trying to run a test step that involves executing a Groovy script for data encryption, but I'm getting a bunch of errors as a result.

I have downloaded (from Maven) and copied all the following jar files required by the script provider into SoapUI's lib directory :
bcprov-ext-jdk14-1.47.jar, bouncycastle-jce-jdk13-112.jar, common-lang3.jar, nimbus-jose-jwt-8.2.jar, nio_char-src.jar, nio.jar, org.json.jar, slf4j.jar.

As the required versions of these .jar files are obsolete, but respecting their names seems mandatory, I tried to :
-copy the latest version of each .jar file without changing its name: same errors
-copy the latest version of each .jar file and change its name to the expected older version: same errors.

Start of script :

Errors :

Thank you in advance for any help on the subject