In short: The message is telling you to stop using whatever browser you are currently in and switch to Safari.

“I wanted iOS 17 beta. I clicked the link from my Gmail app on my iPhone. It opened an in-app browser. Error: ‘Download iOS version – please open via Safari.’ I copied the link, pasted into Safari, and it worked instantly.”

Only use this method if you trust the source . Installing profiles from unknown websites can expose your data to security risks. If you are unsure about the website, do not proceed with the installation.