Please upload a debug log and post just the token URL that is generated after the log is uploaded by running the following command from the Pi-hole host terminal:
# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
portainer/portainer-ee latest 4b6f6ed10535 2 months ago 287MB
pihole/pihole latest d87a7e0b3404 3 months ago 239MB
diginc/pi-hole-multiarch debian_armhf b74d2dc9b17c 5 years ago 314MB