I also got this error and fixed it (Spent whole 2 days)
Step 1:Firstly you need to open the notepad as adminstirator .
Step 2:Select file on the notepad and click to open .
Step 3:Go to this directory %systemroot%\System32\drivers\etc\hosts
Step 4:You probably have something like that 54.14.531.953 launchermeta.mojang.com
Step 5:Delete the numbers and launchermeta.mojang.com (I recommed not leaving any spaces )
Step 6:Save the notepad .
Step 7:Delete the modpack you were trying to install and reinstall .
I also got the same error and the staff member of Technic Launcher's discord helped me .If this method didn't work go to Technic's discord server I'm sure they will try to help .