Please share your site's admin credentials, so we will be able to check this issue.

I add admin credentials.

Let me know have you done any kind of customization in site or any changes made recently.

In payplans I did not change anything. Joomla is also not moved.

Hello,

Please provide me super admin access to site and attach ftp details also.
Can i re-install payplans again on your site ?

I add ftp details and change joomla user to super admin. You can re-instal payplans.

You have removed the admin credentials, please add them again.

Now is ok

No, still blank, please cross check it again.

It seems routing issue , because payplans is also not accessible from payplans, it's not payu app issue only.
Generally this issue happen if some customization in code and payplans menus not created properly.

Please submit admin credential again , so i'll be able to rectify this issue.

The joomla account I have given has administrator privileges and super user

Hello,

I checked your site and found that this issue is coming with url rewriting mode.
It may be htaccess issue but we need to confirm by debugging the code, this time ftp is removed only admin details are there.

Please update your site details on this page http://stackideas.com/dashboard/site , so it will not lost and you don't need to fill it again.

Also let me know are you facing 404 error on other pages expect PayPlans Pages.

I have not met the 404 error on other pages.
I added the login data to the specified address

Hello,

After check further again, as long as the URL contain index.php, it will hitting this 404 error, you can try access this joomla registration page URL on your site.
[gist type="php"]
http://yourdomain.com/index.php?option=com_users&view=registration (replace to your site domain)
[/gist] ,
it will redirect back to Joomla login page is because your site doesn't enable allow user registration on your site, you can refer on this screenshot here : http://take.ms/ZW9Nu

If you trying to access this URL without index.php
[gist type="php"]
http://yourdomain.com/?option=com_users&view=registration (replace to your site domain)
[/gist]
, it will redirect to the correct login page without hitting error.

From what i see, I suspect your server restricted access for those redirection URL which contain index.php, can you consult with your webhosting provider regarding this and see whether I mentioned that thing is true?

by the way, we already applied some fix into your site, it should work fine now.