Inventory Product Uploading Issue

[am_209975]

I am working on a Node.js project, and I'm trying to upload products using the Inventory API in the sandbox environment. In the "OAuth Scopes for your app" section, I have the scope https://api.ebay.com/oauth/api_scope/sell.inventory, which is associated with the Authorization Code Grant Type. However, when I run the API, I always receive the following error:

eBay API Error: {
  status: 400,
  data: {
    error: 'invalid_request',
    error_description: 'request is missing a required parameter or malformed.'
  }
}

Could you please help me identify the issue?

Code:

    static async getEbayAccessToken() {
        const { EBAY_CLIENT_ID, EBAY_CLIENT_SECRET, EBAY_ENVIRONMENT } = process.env;
        const baseURL = EBAY_ENVIRONMENT === 'sandbox'
            ? 'https://api.sandbox.ebay.com'
            : 'https://api.ebay.com';
        const tokenUrl = `${baseURL}/identity/v1/oauth2/token`;
    
        const credentials = `${EBAY_CLIENT_ID}:${EBAY_CLIENT_SECRET}`;
        const encodedCredentials = Buffer.from(credentials).toString('base64');
    
        try {
            const response = await axios.post(
                tokenUrl,
                'grant_type=authorization_code&scope=https://api.ebay.com/oauth/api_scope/sell.inventory',
                {
                    headers: {
                        Authorization: `Basic ${encodedCredentials}`,
                        'Content-Type': 'application/x-www-form-urlencoded',
                    },
                }
            );
    
            console.log('Access token retrieved successfully:', response.data);
            return response.data.access_token;
        } catch (error) {
            if (error.response) {
                console.error('eBay API Error:', {
                    status: error.response.status,
                    data: error.response.data,
                });
            } else {
                console.error('No response from eBay API:', error.message);
            }
            throw new Error('Failed to fetch eBay access token.');
        }
    }