Google Workspace has a free shared mailbox too — it's just called a Group
Google Workspace bills per user, and there is no product called a shared mailbox. People conclude that a second inbox means a second seat, and for a portfolio of domains that is the end of the conversation. It shouldn't be: Google Groups do the same job, cost nothing, and there is no limit on how many you create.
A Group is an address. Mail sent to it is delivered to its members, and with a collaborative inbox switched on it also gets conversation assignment, resolved and duplicate states, and a shared archive — which is more than a Microsoft shared mailbox gives you out of the box. Add your licensed account as a MANAGER and you receive the mail in your own Gmail, where you were already looking.
The half everyone misses is send-as. Being a member lets you read; it does not by itself let you answer as the address. Gmail's "send mail as" makes hello@kibipay.com an option in your From selector, and because the domain is inside the same Workspace, Google skips the confirmation email an outside address would need. Without this step you have an inbox you can read and not reply from — which looks like it works until the first customer gets an answer from your personal address.
There is one setting that decides whether any of it functions: whoCanPostMessage. A Group created with defaults accepts mail only from inside your organisation, so every customer email bounces. The group looks completely healthy in the Admin console while doing it. Set it to ANYONE_CAN_POST and allow external members, or you have built an inbox that only your colleagues can reach.
Secondary domains are free on a Workspace subscription — 600 of them — so the pattern scales the same way the Microsoft one does: add the domain, verify it with a site-verification TXT, point MX at Google, create a Group, add your seat, grant send-as. Six steps, per domain, forever.
That repetition is what inboxroot removes. It also handles the one thing Google genuinely won't automate: DKIM keys are minted only in the Admin console, with no API behind them. We generate every other record for you and are honest about that one — the console tells you it needs a human, links to the exact page, and takes the pasted value back into the record set.