Impossible to register for a free account for Ubuntu PRo

### Summary

when trying to register for a free ubuntu account (https://ubuntu.com/login?next=/pro/dashboard?), I land to 502 Bad Gateway nginx/1.14.0 (Ubuntu)
Same when I try to go to [Your subscriptions](https://ubuntu.com/pro/dashboard) [Account users](https://ubuntu.com/pro/users)

### Steps to reproduce the behavior

1) go to https://ubuntu.com/pro/subscribe
2) click on either "register" big green button,
2bis) or click in the footer on [Your subscriptions](https://ubuntu.com/pro/dashboard) [Account users](https://ubuntu.com/pro/users)

### Expected behavior

Should lead me to the register form

### Browser/device details

MacStudio, MacOS 26.5.2 (25F84)
Chrome, Version 150.0.7871.182 (Build officiel) (arm64)

### Reported from

https://ubuntu.com/pro/subscribe

Reproduce the failure from https://ubuntu.com/pro/subscribe and verify the register, Your subscriptions, and Account users links. Trace the affected website routes and nginx gateway response; done means each route reaches the registration or account page instead of returning 502 Bad Gateway.

Written by the indexing model from the issue text.