Some supplier feeds may require additional HTTP request headers before their web server will accept the request.  REST API endpoints will typically require additional information in the headers.

This is probably the case if you get an HTTP 400 Bad Request or HTTP 403 Forbidden error.

You'll need to check with your supplier which specific HTTP headers are required when making a request to their web server.

You can include these headers in the HTTP request in the Data Feed settings under Source Data when selecting the "Web (HTTP/HTTPS)" feed type:

The headers must be in JSON key/value pair format like this below:

{"User-Agent": "ez-inventory", "Authorization": "Bearer 12345"}

The Authorization header in particular is commonly used for authentication.  So if you receive a 403 Forbidden error, it's a good idea to check with your supplier if they require authentication via this header.  You'd typically use this header to provide an access token or API key.