Very late response, but posting for reference.
I had a similar problem in 2019.
I simply removed the SFP module from the Glide supplied Zyxel router and plugged it into an SFP WAN port on my Draytek 3900.
Noting the SFP module came from FS.com, I sent their support a photo of its label. They were able from the serial number to identify which specific vendor personalisation it had and thus identify it precisely.
https://www.fs.com/uk/products/39143.html
Enabling me to source spares...
The 3900 seems to happily work with both generic modules and those with Cisco compatible firmware, so the specific firmware variant seems to be more of a concern if you are using equipment from one of the vendors FS list.
Aside: Now switched to Glide leased line service and use different SFPs.
