The most common reason for echo is a meeting attendee's built-in speakers re-broadcasting audio over their built-in microphone. A quick fix is for anyone not speaking to toggle off their mic. Then as people turn on their mics again one-by-one, you may be able to tell where the echo is coming from. This is also why we encourage the use of headsets because they often have better echo cancellation than many built-in microphones.
Another thing for meeting attendees to check is to go to their gear icon in the upper right of Sococo and confirm that under the camera section the icon showing sound has a line through it. If it does not, click the icon to toggle off the sound.
If you have ruled out the above factors, the next time you are in a meeting where you are hearing echo, please go to the ≡ menu icon at the top left of Sococo > Report a Problem to file a ticket. In the message box, please indicate the specifics (e.g. "I hear myself echo when I speak" or "Jane is speaking and others in the meeting hear Jane echoing").