[SalesForce] Access debug log messages

Found it it in the Tooling API -

TraceFlag
Represents a trace flag that triggers an Apex debug log at the specified logging level.

• To set up a log for a specific user, set ScopeId to null and TracedEntityId to the ID of the user. This option can only be configured for a user, not an Apex class or Apex trigger.
• To configure logging levels for system logs (visible only to you), set ScopeId to user and TracedEntityId to the ID of the logged-in user.
• To set up a system log (visible only to you) for a specific Apex class or trigger, set ScopeId to user and TracedEntityId to the ID of the Apex class or trigger.

There is a good explanation in the answer to Debugging logs in Developer Console is not working

I have faced this issue, which I fixed it by deleting all debugs logs from developer console.

1. In dev console, Select tab "Query Editor" at the bottom of the console
2. Select check box "Use Tooling API"

3. Use this query:

   SELECT Id FROM ApexLog
   

4. Delete all rows (Use shift key to select all rows)

https://help.salesforce.com/articleView?id=000194045&type=1

Once all rows are deleted you will be able to save new debug logs.

Update : Salesforce has released a video tutorial for same. https://youtu.be/rwORE5T39C4