@Edda It sounds like the script is a RestLet maybe? Regardless of if you want to deploy via bundle or manually, to troubleshoot you can look at the script records to see what they look like (as admin Customization > Scripting > Scripts, may be different in different roles). All script records will have a file. You'll want to be sure that file is in the Sandbox. Look through the rest of the script record, if the script was written in 1.0, you will need to manually define on the record the Get, Post, Delete, and or Put functions as well as library files. 2.0 takes care of that in the script. Also check the parameters tab as there are frequently settings there to check