How to pass issue field values to web panel request

I’m working on adding a web panel to my agent issue view that will retrieve additional information from our own database based on a issue field value. Is this even possible with cloud products?

I’ve tried accessing the field using the issue notation as {issue.customer-id} and with the module key as {module-key_customer-id}. However, since the file is a json file I’m unsure how it is being parsed so I haven’t found the proper combination yet.