Could you use your browser's developer tools requests or network tab? You can usually see the errors there.
Chrome: https://developers.google.com/web/tools/chrome-devtools/profile/network-performance/resource-loading
Firefox: https://developer.mozilla.org/en-US/docs/Tools/Network_Monitor
Safari: https://developer.apple.com/safari/tools
It should be safe until you reach a lot of people and get tons of visitors. I advise to get a license as soon as you get some money from donations, or things you sell etc.