Certificate is invalid - it belongs to adalo.com, and there should be a separate cert for app.boatbuddies.se.
I assume Adalo uses Certbot w/Lets Encrypt certificates. Such error happened to me once, but it disappeared shortly after. I don’t remember quite well what I did - may be I re-created the domain in Adalo and waited for 5-10 mins (so that new cert is re-installed).