You might find that even when there is a MOX rule with a higher priority matching, a lower priority MOX rule matches and executes. This article explains the reason why this happens.
MO External rules (MOX) and MO rules (MOR) are evaluated in different ways.
The MOR rules are evaluated following their priority, stopping the evaluations once there is a match. The routing action for that rule is then executed.
All the MOX rules are evaluated following their priority regardless if there is a match or not. The RTR keeps a list with all rules that satisfied the conditions and had a match and then executes the action for every rule in that list.
E.g. to avoid messages to emergency numbers to be charged, you will need to add additional conditions in the specific MOX rules sending the message to the PBC, like a recipient not present in an emergency numbers list. This ensures that only prepaid traffic to any number other than emergency numbers will be sent to the PBC.