JSON: The response is not a valid JSON response
https://wordpress786.com/updating-failed-error-message-the-response-is-not-a-valid-json-response/
Mail not sent: https://www.hostpapa.co.nz/knowledgebase/fix-wordpress-not-sending-email-issue/#:~:text=Download%2C%20install%20and%20activate%20the,emails%20via%20SMTP%20is%20selected.