Here is the meaning of different priority base on its level
Priority level (AVL packet priority) can be:
Module doesn't make additional record.
Module makes an additional record with an indication that the event was caused by an I/O element change (depending on Operands configuration).
Module makes an additional record with High priority flag and sends event packet immediately to the server using GPRS.
This priority triggers same actions as High priority, but if GPRS fails, it sends an AVL packet using SMS data if SMS data sending is enabled and the number is provided in SMS/Call Settings.
Here is the wiki link : FMC130 I/O settings - Wiki Knowledge Base | Teltonika GPS (teltonika-gps.com)