This error often occurs due to a mismatch in the protocol used for API endpoints. For instance, if your backend server is running on http (e.g., http://localhost:5000/[YOUR_Endpoint]), but you mistakenly use https in your API endpoint (e.g., https://localhost:5000/[YOUR_Endpoint]), you are likely to encounter the Failed to load resource: net::ERR_SSL_PROTOCOL_ERROR error.

To resolve this, ensure that the protocol (http or https) in your API requests matches the one your server is configured to use. If your server is not set up with SSL/TLS, make sure your requests use http instead of https.