OK, put the bottom layers back because kibot assumes they are there.

Ensure CPL filenames are unique for top and bottom.

Author: jonathanpallant

Kicad/.kibot/gerbers_jlcpcb.kibot.yml

@@ -113,7 +113,7 @@ outputs:
     type: position
     options:
       variant: rotated
-      output: "%f-%r-cpl.%x"
+      output: "%f-%r-%i.%x"
       format: CSV
       units: millimeters
       separate_files_for_front_and_back: true

Kicad/neotron-pico.kicad_pcb

@@ -1,7 +1,7 @@
 (kicad_pcb (version 20211014) (generator pcbnew)
 
   (general
-    (thickness 1.60652)
+    (thickness 1.61652)
   )
 
   (paper "A3")
@@ -19,9 +19,13 @@
     (1 "In1.Cu" power)
     (2 "In2.Cu" power)
     (31 "B.Cu" signal)
+    (32 "B.Adhes" user "B.Adhesive")
     (33 "F.Adhes" user "F.Adhesive")
+    (34 "B.Paste" user)
     (35 "F.Paste" user)
+    (36 "B.SilkS" user "B.Silkscreen")
     (37 "F.SilkS" user "F.Silkscreen")
+    (38 "B.Mask" user)
     (39 "F.Mask" user)
     (40 "Dwgs.User" user "User.Drawings")
     (41 "Cmts.User" user "User.Comments")
@@ -31,6 +35,7 @@
     (45 "Margin" user)
     (46 "B.CrtYd" user "B.Courtyard")
     (47 "F.CrtYd" user "F.Courtyard")
+    (48 "B.Fab" user)
     (49 "F.Fab" user)
   )
 
@@ -46,6 +51,9 @@
       (layer "In2.Cu" (type "copper") (thickness 0.0152))
       (layer "dielectric 3" (type "core") (thickness 0.2104) (material "FR4") (epsilon_r 4.6) (loss_tangent 0.02))
       (layer "B.Cu" (type "copper") (thickness 0.035))
+      (layer "B.Mask" (type "Bottom Solder Mask") (color "Green") (thickness 0.01) (material "Liquid Ink") (epsilon_r 3.3) (loss_tangent 0))
+      (layer "B.Paste" (type "Bottom Solder Paste"))
+      (layer "B.SilkS" (type "Bottom Silk Screen") (color "White") (material "Liquid Photo"))
       (copper_finish "ENIG")
       (dielectric_constraints yes)
     )