How do replace carriage returns (newlines) in one of my variables in an alert action to make it JSON compliant?

I'm sending JSON in one of my alert actions to a REST API.

I've formatted the JSON and I'm also using variables (like ${N=Alerting;M=Notes} ).

Unfortunately, the Alert Notes variable value has some unsafe JSON characters in it (namely, carriage returns).  My REST API is giving me these errors from time to time:

There was an error when trying to parse the webhook body to JSON (could be due to un-escaped control characters like newlines):
Illegal unquoted character ((CTRL-CHAR, code 9)): has to be escaped using backslash to be included in string value at [Source: (ByteArrayInputStream); line: 3, column: 422] (through reference chain: com.codebarrel.automation.api.webhook.IncomingWebhook["Description"])
I'm stumped on how I can replace the newline character embedded in the ${N=Alerting;M=Notes} value?  Is there a built in replace function?
Thank you~!