i wanted to use the synchronized data extensions in the journey but they are not coming, i have synced the account and contact entities in my mc instant but cannot see them in journey
Check the Synchronized Data Extension to ensure that the Synchronization is working and the record is available in the DE.
If that's good, check the Event Performance for the Journey to understand if the records are being evaluated by the Journey. See the screenshot below. Dig deeper to get the audit trail for where the error is. I hope this helps.