Yes that’s a clue. Go to the “Advanced Settings” menu of the plugin and then uncheck the “Enable Legacy Checkout API” checkbox and save the settings. Stripe is slowly discontinuing their old API usage. So you need to make sure to use the new API (which our plugin supports).
Also, go to your stripe merchant account dashboard and make sure that you are using the latest API in your account.
On a side note: Looks like you may have switched your site to use SSL certificate but you are not enforcing that all pages be loaded using the “HTTPS” URL. Do the following:
1) Check all the settings field to see if there is any URL that is using a non-https URL. If it is then update that URL value to use the “https” URL and save the settings.
2) Use a plugin like the following to force all pages on your site to be loaded using the HTTPS version: