if (afi ipv4 && protocol bgp) {
  jump GLOBAL-DENY-v4;
  if (bgp-as-path ^123$) {
    set bgp-local-pref 200;
  }
  set bgp-communities TRANSIT;
  set bgp-ext-communities rt:123:111.111.111.111;
  accept;
}

[admin@MikroTik] /routing/filter/community-ext-list> add list=yes communities="rt:123:123"                    
[admin@MikroTik] /routing/filter/community-ext-list> add list=yes communities="rt:123:123.123.123.123" 
invalid value for argument community:
    invalid prefix route distinguisher value
    value of raw contains invalid trailing characters