Google announced it is now limiting the number of service areas a business can list to no more than 20. Google wrote in the Google Ads Help page "service area businesses are now limited to having a maximum of 20 service areas per business."
Google added the limit, which was previously not listed at all, on the help document, which now reads "you can add up to 20 service areas."
What if you need more? Google said they "recommend expanding the existing ones to cover larger areas. You can set your service area based on a combination of entire cities, districts, postal codes, or other areas that you serve."
What if you already have over 20 service areas listed? Google said you will "receive suggested updates to their service areas to cover the same geographic area while only using 20 areas."
Forum discussion at Google Help.