Normally, it is not possible to use commands that invoke a 4D form or dialog on the client when web serving in Non-contextual Mode.

Command Web Services, HTML Support

For example, attempting to use the command DIALOG in Non-contextual mode will result in the following message being displayed to the web user:

"Server Error
An error occurred while processing the request, please try again."
However, the ALERT command will cause the text of the alert to be successfully sent to the web browser. The title of the window will be "4D Dialog" and cannot be customized. This is useful for quick & dirty testing, to avoid having to create & send a small HTML document just to send a diagnostic message to the web browser. Keep in mind that, as stated in the language reference, execution of your 4D method will terminate immediately after a call to ALERT in a Non-contextual web process - so make sure that is acceptable.