Time synchronization via sntp does not work for Shelly PlugS

Hé there, I'm new to this forum. I have a problem with my new Shelly PlugS. Sofar I used Shelly1 devices without any issues for years. Last week, I have installed a Shelly PlugS. I have set a fixed IP address and I'm able to connect via multiple ways. However the time synchronization with a public sntp server fails. I tried several public servers but without any success. As a result I can't use any time scheduling or sunrise/sunset because the actually time is not correct but is uses still the time after startup. Has anyone an idea how to solve this issue? I reboot, reset to factory settings and reinstalled the Plug several times. Configuring by means of Bluetooth, or by the fixed IP address does not make a difference. I updated the firmware to the latest version.
Without the actual time of sntp I'm not able to use timescheduling, I tried it however without any succes. Only using the local time of the Plug will trigger it.
Has someone an idea to solve?

Hi, thanks for your response. I tried with and without the prefix of http://, it doesn't make a difference. I tried several public snpt servers (time.windows.com, time.google.com, local servers e.g. ntp.time.nl etc..) All give the same result, at reboot the Shelly starts at 01.00. Due to the geolocation, 1 hour offset). The logfiles show the connection time and further on the internal shelly time.
Thank you in advance,

The problem is solved, the DNS server was not functioning correctly. Therefore the SNTP server couldn't be accessed.