I need to set inbound REST integration in one of my requirement. Whenever we hit Salesforce URL, it should update some info in Salesforce. I am using GET method and passing parameters in URL.

Here is URL I am hitting from POSTMAN - https://peeke-dev-ed.my.salesforce.com/services/apexrest/SFRen/BreakDownCounter?cust=KonarkRegency&build=A&wTank=T1&wLevel=50

But this gives me error - "errorCode": "INVALID_SESSION_ID"  

When I hit URL(/services/apexrest/SFRen/BreakDownCounter?cust=Greenland County Narhe Gaon&build=A&wTank=T1&wLevel=50) from workbench, it updates records successfully. 

My Apex Class is-
@RestResource(urlMapping='/BreakDownCounter/*')
global with sharing class RESTBreakDownController {
    @HttpGet
    global static void updateWaterLevels(){        
        String accntName=RestContext.request.params.get('cust');
        String buildName=RestContext.request.params.get('build');
        String tankName=RestContext.request.params.get('wTank');
        String waterLevel=RestContext.request.params.get('wLevel');
        
        SFRen__Water_Tank__c wTank=[select Id, SFRen__No_of_Times_Emptied_in_a_Day__c , SFRen__Building__c, SFRen__Max_Capacity__c, SFRen__Today_Water_Use__c, SFRen__Current_Water_Level__c, SFRen__Building__r.SFRen__Account__r.Name, SFRen__Building__r.Name from SFRen__Water_Tank__c where SFRen__Building__r.SFRen__Account__r.Name=:accntName and SFRen__Building__r.Name=:buildName and Name=:tankName limit 1];       
        
        if(wTank!=null){
            SFRen__Tank_Level__c level=new SFRen__Tank_Level__c(SFRen__Reading_Time__c=System.now(),SFRen__Water_Level__c=Decimal.valueOf(    waterLevel),SFRen__Water_Tank__c=wTank.Id);       
            insert level;            
        }       
    }   
}

I am not using any authentication. Am I missing anything in the process? Any help would be much appreciated. Thank you in advance.