Abhijeet,
This is likely a mismatch in the GUID values. Please follow the below steps.
1. Login to the Policy Manager
2. Right click on "Account Plans Fragment" and click "Policy Properties"
3. Copy the value of "Policy GUID"
4. Click on "Tasks" > "Manage Cluster-Wide Properties"
5. Open the cluster-wide property titled: portal.account.plans.fragment.guid
6. Ensure that the value of this cluster-wide property matches the value from Step 3. If it doesn't, replace the value in the cluster-wide property with the value from step 3. Ensure there is no extra white space.
7. Click OK
8. Re-Test the "Sync Account Plans"
-Alec Daniello
APIM Support