Well, desperate times, require desperate measures.
What ended up working for me was:
In the SFP stick use the router’s MAC and SN:
/system/misc
eqsn set "YCEC33333333"
mac1 get
pon_passwd set cc11bb5511ee
register_id set cc11bb5511ee
mac1 set cc:11:bb:55:11:ee
exeep_w8 0 "cc11bb5511ee"
On Unifi WAN set:
VLAN ID: 131
MAC Address Clone: <ONT MAC> (this is not the router's MAC)
I finally got an IP address and I got internet!