Welcome and thank yo for sharing your experience!
You do nothing wrong...
Try this (from the kamoj FAQ):
Q: As soon as I open or interact with OpenVPN or DNS Privacy/Ad-Blocking I get a admin/password request
pop up which only goes away after I click cancel, and I'm sent to the password reset page.
I have tried different browsers and privacy modes with same issue.
A: That problem others have even with Netgear stock firmware (You can search Netgear forum a.o.).
Netgear has had many problems with different character sets through the years and their html code is a
"jungle" of tries to fix it.
I have not been able to correct the issue in the add-on yet - sorry!
A solution is to CHANGE password (NOT just enter your old credentials), or it will stay bad until you do.
Use a password without non-alphanumeric characters. Especially "$" should be avoided.
You should try to not use any of these characters in the password:
"Non-English-characters,$,!, <, >, @, %, *,?, .,+,-,/,|,\,&,=,',",`,´"
If it starts working then add "strange" characters one by one till you find out the "bad" one.
I have one silly question: I try to enable HDD Spin down but when I check it and selecting 20min the logon window pops up and immediately disappears with Chrome. With Opera I can enter my password and username but then it asks me to enter the routers serial to reset password.
What I do wrong?