A 403 response is not caused by file permissions (chmod). Unless you broke the file permissions and make the file unreadable, it’s not going to fix it. So if you didn’t touch the file permissions before, please don’t touch them now. At best it will do nothing, at worst you’ll break your account.
These are common reasons why people actually get 403 errors while using our hosting:
If that article doesn’t answer your question, can you please point out which exact URLs cause this issue, or how we can reproduce this issue?