Hi,
So firstly, by default each SMS Utilities rule has Authorization method set to "By router admin password", which indicates, that before actual SMS command, a router's admin password should be entered in the message.
Basically message should change from:
cellular apn=ipfija.vodafone.es
to:
Admin123 cellular apn=ipfija.vodafone.es (if router's admin password set to Admin123).
Also,
There seems to be the issue with SMS commands in firmware version RUT9XX_R_00.05.03.3, it is indicated in other question here, (or the issue might be related only to SMS reboot) so if you're using this firmware version, you might need to wait for the new firmware release.