Hello @mirek,
We apologise for the delayed response.
Indeed, yesterday we experienced issues with our API.
You probably received a notification on the email address you are using with your Stuart account.
If this is not the case you can reach out to cse@stuart.com and we will be able to add you to the list in order to receive such notifications in the future and to receive the postmortem that we will be releasing in the next few days.
For more information on related Tips & Best practices please see our post Incidents & Outages
Thank you for your understanding