Subscription Management: improve error message when confirmation process fails

[liviopv]

In support, it's not uncommon for us to talk to users who are having trouble subscribing to their own site using a secondary email address.

When they invite themselves or fill in the subscription form, they don't expect to have to log out of their account or open the confirmation link in a private window to be able to complete the process. This also exposes the site owners to our subscription flow, which is still very problematic as mentioned in #32742, #32396, #32396.

Currently, the message shown to these users is too open-ended and it doesn't make it clear what the error is, leading to frustration and support requests:

Your subscription could not be activated. It may have expired, or the email address you subscribed with is not attached to your WordPress.com account.

Steps to reproduce

1. Follow a site owned by you with a secondary email address
2. Open your email to confirm the subscription/accept the invitation while logged into your primary WordPress.com account
3. You will be taken to 4C8E-p2 for your WordPress.com account, without anyway of confirming/accepting.

What I expected

I expected that I should be able to confirm a subscription or accept an invitation sent to different email address regardless of the WordPress.com account I'm currently logged in.

What happened instead

I had no way of accepting the invitation without logging out or opening in a private browser window, and I had no indication that it's what I should do.

Screenshot / Video

Screenshot: https://d.pr/i/TcZPmV

Context / Source

#journey #reallife #stresscase #painpoint.

#user-report

[github-actions]

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[inaikem]

Trying to replicate for WPcom Triage but have yet to receive my confirmation email. I'll be back to complete testing as soon as I can.