put https://api-sandbox.modulrfinance.com/api-sandbox-token/customers//notifications/
If you need to change anything about a particular notification, for example add an email address or make it inactive, then this is the endpoint to use. You need to put all of the information into this request for the notification even if it isn't changing, so either you will need to record this somewhere when you create the notification, or call the 'GET' request first.