It worked for me the last 3 times, but not this time. I get the contact your local office message. I have renewed my Retirement Extension since the last time it worked.
I tried Microsoft Edge and Google Chrome to no avail. I've tried for 3 consecutive days, starting from 12 days before due date, still no luck.
Eventually I rang the Immigration Hotline and the lady tried to be helpful, taking me through the possible reasons, such as new passport, leaving the country, trying a different browser. Then she gave up and supplied me with the telephone number of my local immigration office, but I've decided just to go there and get it done.