Challenge Not yet complete... here's what's wrong:
The WarehouseCalloutService class does not appear to have run successfully as the equipment records are not found in the database. The REST endpoint returns 22 records so your org should have at least 22 records in the Product2 table. Make sure that you successfully run this class at least once before attempting this challenge. Since this class is implementing the queueable interface, you may want to wait to ensure that it has processed successfully.

public with sharing class WarehouseCalloutService implements Queueable, Database.AllowsCallouts {
    
    private static final String WAREHOUSE_URL = 'https://th-superbadge-apex.herokuapp.com/equipment';
    
    /**
	 * Queue process execution
	 */
    public static void execute(QueueableContext context){
        syncWarehouseAndSalesforceDB();
    }
    
    /**
	 * Synchronize Warehouse Data to Salesforce database. 
	 */
    public static void syncWarehouseAndSalesforceDB() {
        // Send GET request to Heroku
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint(WAREHOUSE_URL);
        request.setMethod('GET');
        
        HttpResponse response = http.send(request);
        if (response.getStatusCode() == 200) {
            // Get request result body
            List<Object> results = (List<Object>) JSON.deserializeUntyped(response.getBody());
            // Create equipments to insert
            List<Product2> equipmentsToInsertList = new List<Product2>();
            for (Object equipment :results) {
                // Parse object to String, Value map
                Map<String, Object> equipmentMap = (Map<String, Object>) equipment;
                
                Product2 equipmentToInsert = new Product2(
                    Cost__c = (Decimal) equipmentMap.get('cost'),
                    Lifespan_Months__c = (Integer) equipmentMap.get('getlifespan'),
                    Maintenance_Cycle__c = (Integer) equipmentMap.get('maintenanceperiod'),
                    Name = (String) equipmentMap.get('name'),
                    Current_Inventory__c = (Integer) equipmentMap.get('quantity'),
                    Replacement_Part__c = (Boolean) equipmentMap.get('replacement'),
                    Warehouse_SKU__c = (String) equipmentMap.get('sku')
                );
                
                equipmentsToInsertList.add(equipmentToInsert);
            }
            System.debug(equipmentsToInsertList);
            // upsert equipment
            upsert equipmentsToInsertList Warehouse_SKU__c;
        }
    }    
}

System.enqueueJob(new WarehouseCalloutService());

// return 22 records found
SELECT COUNT() FROM Product2

The tests also run successfully. 
I've also checked that I am using the correct Playground environment for the validation.

Could someone explain to me what's wrong ?