Why is i.cluster not recognising my input imagery subgroup?

I’m trying to do an unsupervised image classification in Grass 7.8. Here is what I have done so far:

1. Imported my aerial photography (GeoTIFF)
2. Set the region
3. Recreated the full colour image using r.composite
4. Recombined the image layers using i.group (created a subgroup with just the r, g, b bands)

Here is my problem: when I now try the unsupervised classification process with i.cluster I select the subgroup image that I just created using i.group. But when I click "Run" I get the following Error message "Error in i.cluster Parameter ‘subgroup'(name of input imagery subgroup) is missing".

Does anyone know what I’m doing wrong?