If you are adding a provider or facility to your estimate, the tool will ask for their Tax ID (TIN) and NPI. If you do not have them, you can skip over them, but it's highly encouraged to obtain the information to give your patient a complete estimate.
Please ensure you review the requirements for Good Fatih Estimates as set forth by CMS.
NPIs can be located on the NPPES website - https://npiregistry.cms.hhs.gov/search