RequestUtils.fetch error: 403 when I try to sign into EndNote Online

I can't use any of the features:

• View PDF
• Download PDF
• Export PDF and reference
• Push reference to EndNote account

The view PDF button just sends me to an error screen on a new tab. The download PDF and export PDF buttons do nothing and I can't sign into my EndNote account; instead, I get a RequestUtils.fetch error: 403. I just tried to use the same login details to login directly to EndNote online and they work just fine.