Error message when submitting

I am using WordPress 5.2 and CF7 5.1.3.

Out of the blue none of my contact forms work. Every time I try to fill out one of my forms I get this error message:

“There was an error trying to send your message. Please try again later.”

I have the Flamingo plugin installed, and the message content does get visible in incoming messages in Flamingo but the error message is displayed anyway…

What could be the reason for this? Please help.

The page I need help with: [log in to see the link]