If you’ve already double-checked that your image URLs are correct, it’s possible that the image host is blocking Bannerbear's access.
If you’re using Cloudflare or another content delivery network, you can try whitelisting the app.bannerbear.com domain to stop your server from blocking the Bannerbear requests.
Alternatively, you can use Bannerbear’s built-in Image Proxy feature as a workaround.
Select Enabled from the Image Proxy drop-down menu