This issue seems to be linked to compatibility issues with secured (SSL) certificates on websites and some browser versions (e.g. Apple / Safari users). Below are some recommendations you can follow to fix this issue:
1) First, try rebooting your device (PC, labtop, tablet of smartphone).
2) If after rebooting this problem continues, try using a different browser e.g. Chrome, Firefox, IE/Edge, etc.
3) If problem persists, try remove cookies and cache on your browser. Below are the steps to remove cookies and cache in Chrome:
Chrome > Settings > Advanced > Privacy and Security > Clear browsing data > Select [ ] Cookies, and [ ] Cached Files, click "Clear Data"
4) If you are still getting this error, try using a different device (PC, labtop, tablet of smartphone).
If Safari is the only browser you can use, we recommend that you read this article and apply some of these tips:
https://blog.pcrisk.com/mac/12572-safari-cant-establish-a-secure-connection-how-to-fix
If after you try the above recommendations the "internal server error" problem continues, please contact us.