SRST unvaliable on ISR4K after register smart licensing.

[Rps-Cheers]

HI  CSC,

We purchased an ISR4K as a voice gateway, and purchased a SRST smart license to allow the phone to register with the voice gateway when CUCM fails. It seems that there is no problem at first, but after we registered the smart license, we can see the "ISR_4xx1_UnifiedCommnnication" license, but did not see the SRST license by using the command "show license status". At this time, I can see that ISR4K is registered in my smart account. When I disconnect the link to CUCM, the phone cannot register to VG and displays "Max Phones Exceeded".
I don't think there is any problem with the device registration, but why the SRST license cannot be synchronized to the device, resulting in phone registration failure. Have you encountered such a problem? How can I solve it?

Thanks & BR