Shortly after the acquisition I logged in to Harvest to send the month's invoices, and found that doing so [without using their payment portal] was no longer possible with a free account.

Annoying, but worth the $10 / month for the basic plan not to have to migrate to another service so I decided to upgrade.

Helpfully there was a "Upgrade your account to send this invoice" button which I clicked. I'd filled out my credit card details and was about to hit submit when I realised the payment total was for more than $10 / month.

Turns out the upgrade flow subscribes you to the Super Mega Deluxe plan, even though the CTA implied it would just do the upgrade necessary to send invoices again.

A scummy dark pattern. I abandoned the upgrade and migrated to Zoho invoice instead.