Hello duy, welcome to Microsoft Q&A forum.
Based on online reports, this appears to be a server-side issue that affected Windows Insider Preview downloads globally. Multiple users from different countries on various ISPs reported similar download blocking during that period, and community discussions suggest Microsoft made some server-side changes that temporarily blocked many downloads, possibly related to fraud detection or anti-bot measures that may have been too aggressive.
Try downloading again now - it may work. If you're still experiencing the error, try downloading in InPrivate/Incognito mode, switch to a different network if possible, or wait 24 hours and try again. Alternatively, you can use the Media Creation Tool as a workaround.