var url = ‘/app/site/hosting/scriptlet.nl?script=customscript_jj_po_rejection&deploy=customdeploy_jj_po_rejection’;
The URL '/app/site/hosting/scriptlet.nl?script=customscript_jj_po_rejection&deploy=customdeploy_jj_po_rejection' assumes that your Suitelet script has an ID of customscript_jj_po_rejection and a deployment ID of customdeploy_jj_po_rejection.
You’ll need to replace these values with the actual IDs of your Suitelet script and deployment. You can find these IDs in the script deployment record or in the URL of the script deployment page.
For example, if your Suitelet script has an ID of customscript_my_suitelet and a deployment ID of customdeploy_my_suitelet, the URL should be:
'/app/site/hosting/scriptlet.nl?script=customscript_my_suitelet&deploy=customdeploy_my_suitelet'