Hi Joost,               one question, please. Can you please tell me where you sourced your 50ohm termination resistors from? I take it these are carbon and not WW? Many thanks, de Spence M0STO

I purchased the pre-built kit and am having almost the exact same problem as described by Pat Patrick Molloy below.  Since this is for 115V AC mains (USA), I removed R9 and installed a jumper across its pads as instructed.  I purchased a SIM card from truphone.com and activitated it, and tested it in an unlocked iPhone 4S.  It worked fine in the iPhone, there is no SIM PIN, I was able to send and receive SMS text messages from there, and was able to make an outgoing call.  However, when the SIM is installed in the Mains Outage Detector, sending the text "Config Remote +1XXXYYYYYYY" (where XXXYYYY is my iPhone X's number) from the iPhone X does not seem to have any effect.  No reply message was received and LED5 continues to blink (albeit at a rate somewhat faster than 1Hz, more like 3Hz).  I followed the instructions in the configuration Notes posted by Lucky above and still couldn't get it to work.  I tried resetting back to default state and re-sent the text several times.  No difference. Sometimes, LED5 and LED2 would stop blinking for a few seconds (they go completely off), but then would resume blinking after that. The attached youtube video shows the board and LEDs' status.  Curiously, removing the batteries (while AC mains is still connected) makes no difference in the LED states. Any idea what's going on and how I could make it work?

Hello.  The folder name wasn't good

Hi cheaptrick, sorry my english is not good, but i try. i had a problem with uploading the webpage with Arduino IDE version 1.8.12, ESP32 Sketch Data Upload Tool. There was a error "esptool not found". After long searching for bug i tryed with Arduino IDE version 1.8.5. I could upload the webpage without error. My "Mini NTP Server" works very good. Perhaps this can help you. Best regards WeLo  

It's good news. BR Claude