I have created a custom Formula field for a Travel object and inserted HYPERLINK formula:
HYPERLINK( "https://apps.fas.usda.gov/visa_requirements/index.asp" , "Link to Foreign Agricultural Service Country Visa Requirements")
It is in the appropriate page layouts. I am Previewing it and when I click on it I get an error message although Syntax is fine.
Image of page layout preview where when clicked the link opens a new browser with error and the URL when clicked goes to this page: