For any foreigner to purchase a property in Mexico, they must have a permit from the federal government. The permit proves that you are in the country legally and documents your status. The permit also states that you will be treated like a Mexican national in the ownership of the property.
The notario will obtain the permit on your behalf, but there is a cost of a few thousand pesos for the processing. It is often referred to as an SRE permit because it comes from the Secretary of Foreign Relations or Secretaría de Relaciones Exteriores.
The permits are property specific so it is impossible to obtain one until you have a property under contract. In addition, an SRE permit is required to have before closing. All of our agents are very well versed in this process and can help you if you would like to connect.