Subscriptions: Improve Messaging when an email has too many Pending subscriptions

[tmmbecker]

Users that have 50 pending subscriptions aren't able to subscribe to any more, but the error message is very vague:

We fixed the error message for those trying to subscribe to a site for which they already have a pending sub in #14326, but the message users see when subscribing to a new site is still very confusing.

Steps to reproduce the issue

1. Start with a WordPress.com account that has at least 50 pending subscriptions.
2. Try to subscribe to a new site.
3. See the confusing error.
4. Remove some of those pending subscriptions from the account.
5. Subscribe again successfully

What I expected

I'd expect to see a message indicating that I have too many pending subs and that's why I'm not able to subscribe, with a link to my subscriptions dashboard where I can remove those pending subs.

Internal ref: 3202604-zen

[htdat]

Actually, we have already handled this case with this PR #14275

There was an error when subscribing. Please try again.

This error message comes from the default case. Maybe another issue happens instead of so many pending subscriptions.

jetpack/modules/subscriptions/views.php

Lines 209 to 211 in be0708a

	default : ?>
	<p class="error"><?php esc_html_e( 'There was an error when subscribing. Please try again.', 'jetpack' ); ?></p>
	<?php break;

[htdat]

Users that have 50 pending subscriptions.

Also, our limit is much less than this now. Ref for A12s 261bc-pb

[tmmbecker]

I'll close this for now.

But it's a bit odd that I got that message, removed a bunch of the pending subs and then was able to subscribe with no error. If it were something else, I wouldn't have expected the error to clear after only removing the pending subs.