Records Aren't Syncing at All
Nothing syncing is a different problem from individual records failing. Work down this list — it's ordered by how often each turns out to be the cause.
1. Is the sync running?
Configuration → Home → Sync History. No recent entries means no runs are happening, which points at the schedule rather than your data.
Check the sync hasn't been paused — see Turning the sync on and off.
2. Is the connection live?
Connection Status should read Connected. Expired OAuth is a common cause of a sync that worked for months and then stopped — see Reconnecting an expired Xero connection.
3. Is the licence active?
Licence Status should read ACTIVE. When a trial or subscription expires, Salesforce revokes the package licence: syncing stops and users lose access to TwoCanConnect's objects until it's renewed. See Licence and subscription errors.
4. Is the object enabled?
If one object isn't moving but others are, check it's switched on in Object Settings.
5. Is the direction right?
Records changed in Xero not appearing in Salesforce is expected on One Way — that's what one-way means. Switch to Two Way when ready.
6. Check one invoice
If a particular invoice is the problem, the Self Diagnosis Tool under Help & Troubleshooting explains what's wrong with that record and how to fix it. See Self-diagnose and logging a case.
One object stuck is configuration for that object. Everything stuck is connection, licence or schedule. Knowing which halves the search.
If none of this explains it, log a case with your Org ID and a debug log.
Xero
Real Estate
Equifax