Insert failed. First exception on row 0; first error: MIXED_DML_OPERATION, DML operation on setup object is not permitted after you have updated a non-setup object (or vice versa):

Integer year = 2021, mon=02, day=12, hour=23, min=50;

Datetime dtGMT = Datetime.newInstanceGMT(year, mon, day, hour, min, 0);

String exTimezone = 'America/Los_Angeles';
String dateTimeForamat = 'yyyy-MM-dd HH:mm:ssz';
String schedulerFormat = 'mm:HH:dd:MM:yyyy';
String crnTemplate = '0 {0} {1} {2} {3} ? {4}';

String localFromatted = dtGMT.format(dateTimeForamat, UserInfo.getTimeZone().getId());
String exFormatted = dtGMT.format(dateTimeForamat, exTimezone);

Datetime localDTValueGMT = Datetime.valueOfGMT(localFromatted);
Datetime exDTVaueGMT = Datetime.valueOfGMT(exFormatted);

Integer minDiff = (Integer)(localDTValueGMT.getTime() - exDTVaueGMT.getTime())/60000;

Datetime scheduleDTGMT = dtGMT.addMinutes(minDiff + 15);

String schFormmated = scheduleDTGMT.formatGMT(schedulerFormat);

String cronExp = String.format(crnTemplate, schFormmated.split(':'));

System.debug('dtGMT : ' + JSON.serialize(dtGMT));
System.debug('localDTValueGMT : ' + JSON.serialize(localDTValueGMT));
System.debug('exDTVaueGMT : ' + JSON.serialize(exDTVaueGMT));
System.debug('scheduleDTGMT : ' + JSON.serialize(scheduleDTGMT));
System.debug('cronExp: ' + cronExp);

trigger AccountTrigger on Account (before insert) {

      if(Trigger.isInsert && Trigger.isBefore) {

        
        List<Account> myList = new List<Account>();

        for(Account acct : Trigger.new){
          if(acct.name == 'My Test Account'){
           acct.AnnualRevenue = 0;
           myList.add(acct);
          }
        }

        if(myList.size() >= 0){
          insert myList;
        }
      }   
}

public class OutterClass {
    Public String name = 'outterclass';
    
    public void setName(String name){
        this.name = name;
	}
    
    public class InnerClass{
       Public String name = 'innerclass';
    }

}

//Parent to Child
SELECT Name, (SELECT name FROM Sessions__r) FROM Public_Event__c
//Child to Parent
SELECT id, name, Public_Event_Name__r.name, Public_Event_Name__r.id From Sessions__c

public with sharing class TruncateId {
    public TruncateId() {

    }

    @InvocableMethod(label='Truncate ID' description='Transaction Id on Opportunity Object' category='Opportunity')
    public static void Truncate(List<Opportunity> OppIds){

        ID oppID = OppIds[0].id;

        Opportunity opp = [SELECT id, TranscationId__c, name FROM Opportunity WHERE id = :oppID];

      
        String last6 = opp.TranscationId__c.right(6);
        if(opp.TranscationId__c != null){    
            if(last6 != opp.Name.right(6)){
                opp.name = opp.name + last6;
                update  opp;
            }
        }
      

    }

    public class GetOppId{
        @InvocableVariable(required=true label='Opportunity Id')
        public ID oppID;

    }

}

public with sharing class ContactTriggerHandler {
    //
    // custom trigger handler setup to handler all triggers received on Contact object
    //
    public Boolean isTriggerExecuted = true;
    private boolean myIsExecuting = false;
    private integer BatchSize = 0;

    public ContactTriggerHandler(boolean isExecuting, integer size) {
        myIsExecuting = isExecuting;
        BatchSize = size;
    }

    //
    // On Before Insert
    //
    public void OnBeforeInsert(List<Contact> contactList){
        List<String> emailList = new  List<String>();
        
        for(Contact contact : contactList){
              emailList.add(contact.email);
        }
        
		List<Contact> newContactList = new List<Contact>();
        List<Lead> leadList = [SELECT id,firstname,lastname, email,LeadSource,phone, MobilePhone,OwnerId,HasOptedOutOfEmail FROM Lead WHERE email IN :emailList];
       
        for(Contact cItem : contactList){
            //Merge
            for(Lead lItem: leadList){
            	cItem.HasOptedOutOfEmail = lItem.HasOptedOutOfEmail;
            	cItem.OwnerId = lItem.OwnerId;
            	cItem.LeadSource = lItem.LeadSource;
            	cItem.MobilePhone = lItem.MobilePhone;
				cItem.phone = lItem.phone;
            	cItem.LeadSource = lItem.LeadSource;
           	 	newContactList.add(cItem);
            }

        }
                

    }

    //
    // On After Insert
    //
    public void OnAfterInsert(List<Contact>  contactList) {
       
        List<String> emailList = new  List<String>(); 
        for(Contact contact : contactList){
              emailList.add(contact.email);
        }
        
        List<Lead> leadList = [SELECT id,firstname,lastname, email,LeadSource,phone, MobilePhone,OwnerId,HasOptedOutOfEmail FROM Lead WHERE email IN :emailList];
        List<Task> taskTransferList = [SELECT Id, Who.Id, Who.Type FROM Task WHERE Who.Type = 'Lead'];
        List<Task> taskUpdate = new List<Task>();
        
        for(Contact cItem : contactList){
            //Move Task to Contact
            for(Lead lItem: leadList){
                if(taskTransferList.size() > 0){
                    for(Task taskItem :taskTransferList){
                        taskItem.whoid = cItem.id;
                        taskUpdate.add(taskItem);
                    }
                }

        
            }
            upsert taskUpdate;
            delete leadList;

        }
  
}

trigger ContactTrigger on Contact (before insert) { //Context and Event
   
    if(Trigger.isInsert && Trigger.isBefore) { // Condition
       System.debug(Trigger.new);	// Action
    } 
  
}

(before insert, after insert,before update, after update, before delete, after delete, after undelete)

public class TestClass {
    
    public Static Integer copies = 0;
    
    
    public TestClass(){
        this.add();
    }
    
       
    public void add(){
        copies++;
    } 
    
    public Static void subtract(){
        copies--;
        System.debug(copies);
    } 


}

public class Human {
    public String Name;
    public Integer Age;
    
    public Human(){
      this.Age = 0;
    }
        
    public void setName(String Name){
        this.Name = Name;
    } 
    
    public void setAge(String Name){
        this.Age = Age;
    } 
    
    public void Run(){
        System.debug('Run');
    } 
    
    public void Jump(){
        System.debug('Jump');
    } 
    
    public void Climb(){
        System.debug('Climb');
    } 
}

Human fred = new Human();

fred.setName('Fred');
fred.setAge(18);

fred.Run();
fred.Jump();
fred.Climb();

Map<String,String> theOne = new Map<String,String>();
Map<String,String> theTwo = new Map<String,String>();

theOne.put('task', 'Active');
theOne.put('task2', 'Inactive');
theOne.put('task3', 'Inactive');
theOne.put('task4', 'Inactive');

theTwo.put('task', 'Active');
theTwo.put('task2', 'Inactive');
theTwo.put('task3', 'Inactive');
theTwo.put('task4', 'Inactive');

void toggleActive(String taskName, Map<String,String> taskMap){
    taskMap.put(taskName, 'Active'); 
    for(String key : taskMap.keySet()){
        if(key != taskName){
       	 taskMap.put(key, 'Inactive');
        }
    }
}

toggleActive('task3', theTwo);

System.debug(theOne);
System.debug(theTwo);

@wire(callout2Apex, {id: this.recordId})
function({ error, data }) {
  if (data) {
    this.arr = JSON.parse(data).keyFromJSON;
    this.loaded = true;
  } else if (error) {
    this.loaded = false;
  };
}

public Boolean mapContains(Map<id,Object> searchObj, String searchKey, String searchVal){
	for (ID idKey : searchObj.keyset()) {
		System.debug(searchObj.get(idKey).get(searchKey));
		if( searchObj.get(idKey).get(searchKey) == searchVal) {
			System.debug('Match Found'+ searchObj.get(idKey));
			return true;
		}else{
			System.debug('No Match');

		}
	}
	return false;
}

/* JSON EXAMPLE
{
    "messageId": "PfNxko2cChY94KsiU9cvUL",
    "eventId": "client.updated",    
    "eventSchemaVersion": 1.0,
    "eventInstanceOriginationDateTime": "2022-03-07T00:37:23Z",
    "eventData": {
        "siteId": 123,
        "saleId": 96,
        "purchasingClientId": "100001049",
        "payments": [
            {
                "paymentId": 103,
                "paymentMethodId": 14,
                "paymentMethodName": "Cash",
                "paymentAmountPaid": 300,
                "paymentLastFour": null,
                "paymentNotes": null
            }
        ],
        "saleDateTime": "2018-05-03T16:52:23Z",
        "soldById": 10,
        "soldByName": "Jane Doe",
        "locationId": 1,
        "totalAmountPaid": 150,
        "items": [
            {
                "itemId": 78,
                "type": "Service",
                "name": "10 Punch Pass",
                "amountPaid": 150,
                "amountDiscounted": 0,
                "quantity": 1,
                "recipientClientId": "100000009",
                "paymentReferenceId": 44
            },
            {
                "itemId": 79,
                "type": "Service",
                "name": "10 Kick Pass",
                "amountPaid": 150,
                "amountDiscounted": 0,
                "quantity": 1,
                "recipientClientId": "100000009",
                "paymentReferenceId": 44
            }
        ]
    }
}*/


public class Sale {
public String messageId;
public String eventId;
public Decimal eventSchemaVersion;
public String eventInstanceOriginationDateTime;
public SaleEventData eventData;
}


public class SaleEventData {
public Integer siteId;
public Integer saleId;
public String purchasingClientId;
public List<PaymentDetails> payments;
public String saleDateTime;
public String soldById;
public String soldByName;
public Integer locationId;
public Integer totalAmountPaid;
public List<SaleItemDetails> items;
}

public class PaymentDetails {
public Integer paymentId;
public Integer paymentMethodId;
public String paymentMethodName;
public String paymentAmountPaid;
public Integer paymentLastFour;
public String paymentNotes;
}

public class SaleItemDetails {
public Integer itemId;
public String type;
public String name;
public Integer amountPaid;
public Integer amountDiscounted;
public Integer quantity;
public String recipientClientId;
public Integer paymentReferenceId;
}

Sale mbSale = (Sale)JSON.deserialize(jsonInput, Sale.class);