MOSTLY AI Inc. (USA) uses ADP Total Source as a Professional Employer Organization in the USA for services such as payroll, https://mostly-ai.atlassian.net/wiki/spaces/Public/pages/897125427 and compliance.
If you are hired in the USA:
always keep your profile up to date on ADP (ex. address, phone number, tax info, etc)
become familiar with its “Basic Employment Policies” below: