# 16021: Failed to join conference due to account concurrency limit exceeded Log Level: ERROR ## Description A conference participant could not be created because your account was at or above its concurrent participant limit. This error is different from 16020, which is returned when a conference reaches maximum participant capacity. ### Possible causes * Your account reached the account-wide concurrent participant limit for Voice Conference. The default limit is 5,000 concurrent participants across all conferences in an account. * Your application attempted to create conference participants before earlier participants had disconnected. Creating conference participants via the API counts toward concurrency. ### Possible solutions * Retry the request after active participants disconnect and your account is back under the limit. * Reduce the number of simultaneous conference participant creations in your application. * If you regularly need more concurrent conference participants, contact your Twilio account team to request a higher limit. #### Additional resources * [Voice Conference](/docs/voice/conference) * [TwiML Voice: ``](/docs/voice/twiml/conference)