Issue Summary

Using regular expressions alongwith string processing methods in Sync conditions and Alert Properties to extract the custom field value throws an error saying 

The correct syntax is {{_payload.customField}} or {{_headers.customField}} or {{_url.customField}} 

Example regular expression: 

{{_payload.customFields.customfield_123.get(0).name}} 

or 

{{_payload.customFields.fields.customfield_123.get(0).name}}

Steps to Reproduce

1. Create a custom field 
2. Try fetching this on Operations Sync Alert processing conditions or Alert fields using regular expressions and string processing methods.

Expected Results

It should allow the regular expression to be added in custom field under Alert Fields. 

Actual Results

The below exception is thrown:

The correct syntax is {{_payload.customField}} or {{_headers.customField}} or {{_url.customField}}

Workaround

Use Automations or fetch the value in Extra Properties in string format and add a policy in the team or Globally to filter the alerts.