esp-idf - mqtt ssl example certificate error

Question

I'm having some trouble with mqtt ssl example on esp-idf ESP32.

Example: mqtt_ssl

If I test it with the default broker "mqtts://mqtt.eclipse.org:8883" and default certificate "mqtt_eclipse_org.pem" It works correctly.

If I change the broker with mqtts://test.mosquitto.org:8883 ( https://test.mosquitto.org/ ) and change the certificate using (mosquitto.org.crt (PEM format), it fails and gave me TLS errors:

mbedtls:ssl_tls.c:5757 x509_verify_cert() returned -9984 (-0x2700)

esp-tls: mbedtls_ssl_handshake returned .0x2700
     esp-tls: Failed to verify peer certificate!
     failed to verify peer certificate
     verification info: ! the certificate is not correctly signed by the trusted CA

What am I doing wrong?