This means that your public key is invalid.
You can check it at https://api.telegram.org/bot {token} / getWebhookInfo URL after installation
When I sent the wrong public key - I get
{"ok":true,"result":{"url":"","has_custom_certificate":false,"pending_update_count":6}}
but if I sent the correct public key, I get:
{"ok":true,"result":{"url":"mycorrecturl.com","has_custom_certificate":true,"pending_update_count":6,"last_error_date":1506772578,"last_error_message":"SSL error {337047686, error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed}","max_connections":40}}
source share