The following applies if you are using a private CA to sign the XMPP certificate or manually installing a certificate. From iOS version 10.3 and later, after installing a certificate as a profile, you must also turn on the trust. To turn on SSL trust for that certificate, follow these steps.
- Open Settings > General > About > Certificate Trust Settings.
- Under ENABLE FULL TRUST FOR ROOT CERTIFICATES, turn on trust for the certificate.
If you do not enable this, you might see an error message 'Lost connection to server, Attempting to reconnect'.