ptp master unsupported MX80

Hello forum guys, 

I configured ptp master in ordinary mode on MX80: 

run show configuration protocols ptp
clock-mode ordinary;
unicast-negotiation;
master {
    interface ae1.903 {
        unicast-mode {
            transport ipv4;

However when I verify clock status, I get: 

run show ptp lock-status
Lock Status:

Lock State    : 2 (HOLDOVER)
Phase offset  : 0.000000000 sec

run show ptp master
PTP Master Interface Configured:

Master Interface           Status
ae1.903                    Master, Unsupported

Any idea what would I miss in the configuration?