If you turn on Trace logging, you may see for example:
So when you see error 825, then this is a permission issue. With FileMaker version 19.2 Claris introduced the fmplugin extended privilege. Old files don't have this, so script triggering is allowed for the plugin. But if the file is new, it gets a fmplugin extended privilege. And if that one is not checked, the script trigger is forbidden. But you can mark the checkbox to allow all plugins.
Start Script "DragAction" in file "DragTest" with control Pause
Current file: "DragTest". User "Christian" on host "DESKTOP-CK2F9O6"
Result: 825 (File is not authorized to reference the protected file)
Or you add a specific fmpluginMBSP to only allow MBS Plugin. And you may define this for all or some privileges, so some user may use plugin and some not.
If you are interested in limiting functionality of MBS Plugin for users, feel free to limit functions with Plugin.SetFunctions call. Or limit functions to certain scripts/file/privileges, check the Plugin.LimitFunction function. If you like to know what functions you use, check the Plugin.UsedFunctions function and run it after the solution has been used for a day or so.
See also Tracing MBS Filemaker Plugin, DbgView for watching trace messages live on FileMaker Server, Watching for Errors with MBS Plugin and About controlling plug-in access between files.