I want to upload files from Salesforce to Box

How do I upload a file from Salesforce (Lightning Experience) to Box?

I get the error.

" FATAL_ERROR box.Toolkit.BoxApiException: box.Toolkit.sendRequest() - HttpRequest endpoint must start with: https://api.box.com/2.0 "

Can't I upload using BoxToolkit?
Here is the code snippet which is doing this. 
---
@future (callout=true)
    public static void uploadFile(String fileName, String recordId, Blob file) {
        
        box.Toolkit boxToolkit = new box.Toolkit();
        
        //getFolderId
        String folderId = boxToolkit.getFolderIdByRecordId(recordId); 
               
        // setEndpoint
        String endpoint = 'https://upload.box.com/api/2.0/files/content';
        
        //setParameters
        Map<String, String> parent = new Map<String, String>{
            'id' => folderId
        };
        Map<String, Object> attributes = new Map<String, Object>{
            'content_created_at' => null,
            'content_modified_at' => null,
            'name' => fileName, 
            'parent' => parent
        };
        Map<String, Object> body = new Map<String, Object>{
             'attributes' => attributes,
             'file' => file
        };            
        HttpRequest request = new HttpRequest();
        request.setMethod('POST');
        request.setEndpoint(endpoint);
        request.setBody(JSON.serialize(body));
        request.setHeader('content-type', 'multipart/form-data');
        
        // sendRequest
        HttpResponse response = boxToolkit.sendRequest(request);
        boxToolkit.commitChanges();
    }