"TLS error" indicates that Stripe was unable to establish a secure connection to your server due to an SSL/TLS issue. Try the following:

1. Use a tool such as SSL Labs' SSL Server Test to determine if there are any issues with your TLS certificate or configuration and resolve any issues found
2. Load your domain or Webhook Endpoint URL in your web browser. Then check for any security or certificate errors reported there and resolve any issues reported

One of the most common issues that people encounter is an incomplete certificate chain, which usually means an intermediate certificate has not been installed. Your SSL/TLS provider should be able to provide the missing certificate and instructions for installing it.