Speeddial on *0 from zaptel attached handset

I’ve used ‘*0x’ for a while now, from a SIP phone, and from an ATA (spa3102). I’ve installed
a ZAPTEL card, with 3 FXS ports, and I’ve noticed that *0 cannot be dialled.

If I renumber the speeddial function to *1, or works, but any attempt to dial *0 hangs up

Any ideas? I have a feeling its a zaptel/asterisk issue, but I thought I’d ask here first.