WordPress Dashboard Backend 503 when Plugin is activated

I first started importting the products on May 16th. at first it was importing fine. until an error occur.
When I refresh the page in the backend dashboard it become 503 error. however, the homepage where visitor go is fine. everything works.

when I did the trial and error of deactivating plugins I found that the plugin from Villa theme is the cause of the error. what should I do?