Hii

Error 405 means you have made a mistake i.e either you have refreshed the page or pressed the back button while the transaction was in process. Now you shall wait till 24 hours, either the amount will be refunded or the process will be completed.
Also i would suggest that before you login again to your aiims account, clear the cache of the browser. Even if there is no progress, then i would suggest you initiate a new payment and continue with your registration.
Also if you feel, you can report your problem to the aiims authority on the following email id - aiims.mbbsexam2019@gmail.com

Hope this helps
Thanks!!