Hello,
Thanks for your query,
In the Wiki Teltonika page appears two lists the configurable GNSS sources.
Examples of Non-configurable GNSS source combinations are:
GLONASS + BeiDou;
Galileo + BeiDou;
Galileo + GLONASS;
Galileo + GLONASS + BeiDou;
GPS + Galileo;
GPS + GLONASS + BeiDou;
GPS + Galileo + BeiDou;
GPS + Galileo + GLONASS + BeiDou.
List of configurable GNSS sources:
GPS only
GPS + BeiDou
GPS + GLONASS
GPS + Galileo + GLONASS
In this case, the example combination that you are tried to configure is in the list the Non-configurable GNSS source combinations.
Best regards.