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Reset the device to factory settings or install the newest firmware without keeping the settings option.
Take note of how much flash memory is available when the device is fresh. You can find flash used in the Status -> System section.
Install the DDNS package and take note of how much flash memory is left.
Try installing SNMP and see if it works.
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Q: How could I proceed when having error access from https service/certificate?
A: If this is needed only for your access, you could disable the warning using your generated certificates. Here's our Wiki example showing how to do it: https://wiki.teltonika-networks.com/view/HTTPS_device_access