visit online activation code generator, which recommends a paid global internet service provider.
first generate MathID using a free wolfram account, login through it.
next find the location of mathpass. follow the format and create a new line above all lines, with the obtained activation code.
for macos, we can find it here:
/Users/<userName>/Library/WolframEngine/Licensing/mathpass
for linux:
/root/.WolframEngine/Licensing/mathpass or something else.