1> Vlidation Rule 
AND($RecordType.Name = "payment's", 
ISPICKVAL(Status, 'Close Completed'),
OR(ISCHANGED(Description),OR(ISCHANGED(Origin))
)

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2> To enable this feature, from Setup, enter Process Automation Settings in the Quick Find box, then click Process Automation Settings. Then, select Enable record locking and unlocking in Apex.
The new Approval.LockResult and Approval.UnlockResult classes let you interact with the results of your programmatic record locks and unlocks.


trigger tresLockCase on Case (after insert, after update) {
    set<Id> recordtolock = new set<Id>();
    Id devRecordTypeId = Schema.SObjectType.case.getRecordTypeInfosByName().get('payments').getRecordTypeId();
    if(Trigger.IsAfter){
        if(trigger.IsInsert){
            for(Case oCase : trigger.new){
                if(oCase.RecordTypeId == devRecordTypeId && oCase.Status == 'Close Completed'){
                    recordtolock.add(oCase.Id);
                }
            }
        }else if(trigger.IsUpdate){
            for(Case oCase : trigger.new){
                if(oCase.RecordTypeId == devRecordTypeId && oCase.Status == 'Close Completed' && oCase.Status!= trigger.oldMap.get(oCase.Id).Status){
                    recordtolock.add(oCase.Id);
                }
            }
        }
    }
    list<Id> recordtolock2= new list<Id>();
    recordtolock2.addAll(recordtolock);
    Approval.LockResult[] lrList = Approval.lock(recordtolock2, false);
    
    // Iterate through each returned result
    for(Approval.LockResult lr : lrList) {
        if (lr.isSuccess()) {
            // Operation was successful, so get the ID of the record that was processed
            System.debug('Successfully locked Case with ID: ' + lr.getId());
        }
        else {
            // Operation failed, so get all errors                
            for(Database.Error err : lr.getErrors()) {
                System.debug('The following error has occurred.');                    
                System.debug(err.getStatusCode() + ': ' + err.getMessage());
                System.debug('Case fields that affected this error: ' + err.getFields());
            }
        }
    }
    
}