The flow currently. Customer:

After the last step, we should show some kind of simple confirmation modal that they've purchased a plan and can now insert premium blocks to the editor.
There might be other "thank you for the purchase" visuals around Calypso that we can borrow?
Thanks for the ping @simison. Your best bet would probably be to use a banner of some sort:
https://wpcalypso.wordpress.com/devdocs/design/banner
Maybe something like this:

Fabulous! I like this, so simple! We can use the core notifications mechanism for 1st iteration; super-duper easy.
In the long run, we might turn it into something more "celebratory".
yeah, it's good to start with and use as a base to iterate.
Feel free to drop any copy ideas here.
cc'ing @ranh and @obi2020 for any suggestions here. For a little background, @simison is implementing a new upgrade flow and he'd like to present the customer with some kind of messaging after the purchase is complete and they're returned to the point they initiated the purchase. This message we currently use after an upgrade could be a starting point:

This is how new snackbar updates look like in Gutenberg, instead of green bar on top of the editor:

Good enough for the first iteration but eventually we'll need some design work to make a more celebratory modal when landing back in the editor (like in the screenshot in above comment).
The copy could be something along the lines:
Your site is now on the [WordPress.com Premium / Jetpack Premium] plan.
No need to mention the block name on the first iteration at least.
Just /cc'ing @monikaburman to make sure that this is on her radar for upcoming design needed.
For a first iteration, I think we can:
Could also consider the Notice component which is a bit more prominent (might be appropriate for a plan upgrade). Probably easy enough to switch out one for the other.
Could also consider the Notice component
Oh, good point; I thought those might've been deprecated. I think Notice indeed is more appropriate for this use-case since notice is shown after landing to the page, not after pressing a button in the editor UI (e.g. compared to saving draft or publishing page).
We talked with @chriskmnds that the logic could be placed in a new file in /extensions/shared and imported to extensions/editor.js so that it runs each time editor is initialized.
Added @jancavan as assignee for design work.
cc: @michaeldcain @simison
Snackbars are meant for temporary messages, so I wouldn't use that here. The Notice component is better in the sense that it is more noticeable, but it isn't really appropriate here either.
Purchasing a plan is a big deal to a user, especially one that requires an annual commitment, so this warrants a proper success notification. Either of these two confirmations will work:
@simison @michaeldcain
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Snackbarsare meant for temporary messages, so I wouldn't use that here. TheNoticecomponent is better in the sense that it is more noticeable, but it isn't really appropriate here either.Purchasing a plan is a big deal to a user, especially one that requires an annual commitment, so this warrants a proper success notification. Either of these two confirmations will work:
@simison @michaeldcain