Found this on google, found no solution in the thread, investigated a little more and found what is causing the problem in my case. Apparently Upwork disables the profile of a customer and leaves his job posts up, but broken. An unsuspecting freelancer then comes on to the job application page for that customer, tries to apply and gets this error message.
Upwork website users can confirm this by trying to apply to another job of the same customer and getting the same error.
Upwork API users get a very clear message when trying to retrieve job details.
Just happen the same thing to me. and I found that the proposal is already submitted by me! I mean on the page, you will see the warning message but when you go to the job post, you will see the text "You have already submitted a proposal ".
If all the verification and other issues are resolved, you better clear check the job post again in a new tab instead of just refreshing the same old page. maybe that job is no more exists, or the proposal is already have been placed but now showing in the current page or do it again after clearing the caches and cookies.
Hi, guys! This just happens when a person is in the process of submitting any proposal and this very moment the job is closed or smth like this! So, you're filling the confirmation form and this very moment the job is closed and, of course, when we submit the form we get this very message, because we are trying to access something that has just been expired!