Still got the following problem, It says it cannot edit the file. Is the cause possibly from the variable then, if I just output it without cloudflow behind it, it works.
{ "error": { "code": "File.RenameFileError", "message": "Probleem bij uitvoering van actie Rename. Kan bestandsnaam niet wijzigen \r\n \r\nMicrosoft.PowerPlatform.PowerAutomate.Desktop.Actions.SDK.ActionException: Kan bestandsnaam niet wijzigen ---> System.NotSupportedException: De opgegeven padindeling wordt niet ondersteund.\r\n bij System.Security.Permissions.FileIOPermission.EmulateFileIOPermissionChecks(String fullPath)\r\n bij System.Security.Permissions.FileIOPermission.QuickDemand(FileIOPermissionAccess access, String fullPath, Boolean checkForDuplicates, Boolean needFullPath)\r\n bij System.IO.File.InternalMove(String sourceFileName, String destFileName, Boolean checkHost)\r\n bij Microsoft.Flow.RPA.Desktop.Modules.File.Actions.RenameFilesAction.Execute(ActionContext context)\r\n --- Einde van intern uitzonderingsstackpad ---\r\n bij Microsoft.Flow.RPA.Desktop.Modules.File.Actions.RenameFilesAction.Execute(ActionContext context)\r\n bij Microsoft.Flow.RPA.Desktop.Robin.Engine.Execution.ActionRunner.Run(IActionStatement statement, Dictionary`2 inputArguments, Dictionary`2 outputArguments)\r\n" } }

I have already done almost all possible combinations today with _ or other tests in terms of with or without extension.
Anyone else have a good suggestion?
Thank you in advance