@jwdave-17.BS 

Not every Deco model supports IoT Network. If you can share Update Deco screenshot from your Deco app, I may be able to tell if your AX1500 supports IoT or not. That page will list all Deco models you have in your Deco mesh and their firmware versions.

Example:

  @Alexandre. Does this help? Many thanks

  @jwdave-17.BS 

Yes, it does help. IoT Network appears in firmware 1.2. Your X10 runs on firmware 1.0.6. It does not have IoT Network. See Understand the Differences Among Deco Firmware Platforms

I would recommend returning X10 back to retailer if it is still under return policy. Look for Deco X50 or X55 as addition to your Deco mesh.

  @Alexandre. That is very helpful, thank you. I will do as you suggest.

  @Alexandre. However the X50 and X55 are not available in the UK at the moment, is the X60 ok?

jwdave-17.BS wrote

  @Alexandre. However the X50 and X55 are not available in the UK at the moment, is the X60 ok?

  @jwdave-17.BS 

TP-Link releases same model name with different hardware versions, and then puts inconsistent firmware releases for hardware versions. It becomes confusing.

Deco X60 hardware V3 appears to support IoT, X60 V1 and X60 V2 will not. 

If you can buy Deco from the store, you can inspect the box there and see hardware version printed on the label. Ordering online you would not know unit you get the box - but, again, you can inspect the box and if version is wrong, send it back without unpacking. 

The list of Deco models and their hardware versions supporting IoT: https://community.tp-link.com/en/home/stories/detail/501928

Also: How to find the hardware version on a TP-Link device

  @Alexandre. Thank you, you have been very helpful.