Getting error while publishing extension.

The request for path /v1.0/sandbox/dev/apps?SchemaUpdateMode=synchronize failed with code 422. Reason: Cannot synchronize extension Report2 because a newer version has already been synchronized.

getting above error while publishing etension for Business Central Sandbox.

Sounds weird.

If you make a new sandbox does the error still occur?

Sounds like you’ve used the same GUID for multiple extensions.