Hello タチバナシェリー, 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 the same 715-123130 error 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.