Currently Admin API requests to locked stores return a 420 status code. As of Thursday August 30th this response will change to 423. We're pushing this change in order to reduce ambiguity around the 420 response code and ensure our responses are as accurate as possible.
If you have any questions or concerns, please feel free to reply in the thread below.
Could you provide some clarity on what "locked" means for a store status vs other shop statuses such as frozen or canceled?
I've seen the API return 402 payment required for "frozen" shops, and also 404 I am guessing when a shop cancels.
I don't see a mention of a 420 (or 423) status here: https://help.shopify.com/en/api/getting-started/response-status-codes.