Try Photopea to rasterize them.
Click Edit>Preference>Install Photopea

https://www.photopea.com/learn/other-layers


YouTube Tutorials Here

I don't know how to rasterize in GIMP, and I keep getting that error:

Did not match Human Template Bone - Missing Bone: Hip
Did not match Human Template Bone - Missing Bone: LArm
Did not match Human Template Bone - Missing Bone: LFoot
Did not match Human Template Bone - Missing Bone: LHand
Did not match Human Template Bone - Missing Bone: LThigh
Did not match Human Template Bone - Missing Bone: RArm
Did not match Human Template Bone - Missing Bone: RFoot
Did not match Human Template Bone - Missing Bone: RHand
Did not match Human Template Bone - Missing Bone: RThigh

I use GIMP as my external editor (but not necessarily as a PSD editor). If you're editing individual parts in GIMP, just click file and "Overwrite (whatever the name of your file is)". It will automatically update in the open CTA workspace.

Update: I figured it out. I didn't rasterize the images. Problem solved.

I tried in Photoshop. It didn't work either. I changed the character's eye color, saved in PS then CTA applied changes, but nothing happened... same eye color.

After I've done modifications using Affinity Designer, I usually click 'SAVE" 
and the character in the Cartoon Animator will be updated.
If I saved it in PSD format, then I clicked "Create Character' icon in the Stage Mode to import the character.
When those errors appeared, it could be that the layers for the said 'missing bone' were not there.




YouTube Tutorials Here

Update: I saved as .PSD in GIMP, and then tried to import changes using "Import PSD Assets" but I got these errors:

Did not match Human Template Bone - Missing Bone: Hip
Did not match Human Template Bone - Missing Bone: LArm
Did not match Human Template Bone - Missing Bone: LFoot
Did not match Human Template Bone - Missing Bone: LHand
Did not match Human Template Bone - Missing Bone: LThigh
Did not match Human Template Bone - Missing Bone: RArm
Did not match Human Template Bone - Missing Bone: RFoot
Did not match Human Template Bone - Missing Bone: RHand
Did not match Human Template Bone - Missing Bone: RThigh

Maybe the problem is GIMP, wonder if Krita or another free photo editing program would work?

I am using "Launch to External PSD Editor" to edit colors. I launch the character in GIMP to edit. How do I get these changes to appear in Animator, do I have to save in GIMP as a certain extention?