You can’t put a template inside of a choice because templates have labels, and like the error message is saying, labels cannot be inside of brackets. You will have to put the cc template after the choice, and put a goto inside each choice option
NARR
Do you want to customize your character?choice
“Yes!” {
goto first_label_of_template
} “No” {
goto after_template
}[customization template goes here]
label after_template
[continue your story here]
Replace “first_label_of_template” with the actual first label of the customization template.