This is the response I got from Reolink support. I've asked for an approximate ETA on the firmware update.

This is Iris from the Reolink Senior Support Team! Thanks for reaching out.
 
After the Doorbell camera is added to the Home Hub series, it does not have the Reolink Chime option so they cannot be paired for now. 
 
Please don't worry, we're working on new firmware for the Home Hub to support the Reolink Chime and it'll be available soon. Before that, here are two workarounds:
 
1. Delete the Doorbell camera from the Home Hub to use it as a separate device so that you can pair the Reolink Chime to it.
2. Or you can keep the Doorbell connected to the Home Hub, and use the Home Hub Ring function. After you press the Doorbell, the Hub will emit a loud tune like a chime.

@user_901203979997352_901203979997352
Response from Reolink:
Sorry for the trouble caused.
The new firmware for the Home Hub will be released next month. Please make sure to turn on the auto-update for your Home Hub so that it can be upgraded automatically when the new firmware is ready. Refer to How to Enable Auto Upgrade via Reolink App

@user_901203979997352_901203979997352
Response from Reolink:
Sorry for the trouble caused.
The new firmware for the Home Hub will be released next month. Please make sure to turn on the auto-update for your Home Hub so that it can be upgraded automatically when the new firmware is ready. Refer to How to Enable Auto Upgrade via Reolink App

This is the response I got from Reolink support. I've asked for an approximate ETA on the firmware update.

This is Iris from the Reolink Senior Support Team! Thanks for reaching out.
 
After the Doorbell camera is added to the Home Hub series, it does not have the Reolink Chime option so they cannot be paired for now. 
 
Please don't worry, we're working on new firmware for the Home Hub to support the Reolink Chime and it'll be available soon. Before that, here are two workarounds:
 
1. Delete the Doorbell camera from the Home Hub to use it as a separate device so that you can pair the Reolink Chime to it.
2. Or you can keep the Doorbell connected to the Home Hub, and use the Home Hub Ring function. After you press the Doorbell, the Hub will emit a loud tune like a chime.

Yep I'm getting the same problem. I've raised a support ticket as there is nothing documented to say that Chime & home hub are incompatible. But it is documented and advertised that you can have up to 5 chimes.