Google has announced that as part of the Privacy Sandbox project, they are phasing out the support for third-party cookies in Chrome.
Workarounds
OPTION 1:
Re-enable the Third-party cookies in Chrome.
Step 1. Go to the Chrome Settings.
Step 2. Go to Privacy and security then click on Third-party cookies.
Step 3. Select Allow third-party cookies.
Step 4: Copy and Paste this URL into your browser: "chrome://flags/#third-party-storage-partitioning" and Disable “Experimental third-party storage partitioning".
Step 5: Copy and Paste this URL into your browser: "chrome://flags/#test-third-party-cookie-phaseout" and Disable “Test Third Party Cookie Phaseout”.
Once the application starts working again, refresh the browser.
OPTION 2:
Use an alternate Five9-supported browser.
Only Use another Browser if you are unable to use Chrome with the methods above.