BASH sed does not evaluate array - bash

Question

So i have an array with filenames.
for i in "${!array_FILE[#]}"; do
printf "%s\t%s\n" "$i" "${array_FILE[$i]}"
sed -e "s/\${USERNAME_VAR}/$USERNAME_VAR/" -e "s/\${USERNAME}/$USERNAME/" template > array_FILE[$i].js
done
The printf works and gives me
0 app_calander
1 app_contacts
2 app_search
3 app_index
but the files created are:
array_FILE[0].js
array_FILE[1].js
array_FILE[2].js
array_FILE[3].js
instead of
app_calander.js
app_contacts.js
app_search.js
app_index.js
If you can help me i appreciate it, it has to be changed by index because i have two array and i need to change values at the same index.
My temporary solution is:
filename="${array_FILE[$i]}"
sed -e "s/\${USERNAME_VAR}/$USERNAME_VAR/" -e "s/\${USERNAME}/$USERNAME/" template > $filename.js
but i was wondering if there is a better way!
REAL ISSUE
Now the real issue is when i try to pass a URL
for i in "${!array_FILE[#]}"; do
#printf "%s\t%s\n" "$i" "${array_FILE[$i]}"
filename="${array_FILE[$i]}"
url="${array_URL[$i]}"
sed -e "s/\${USERNAME_VAR}/$USERNAME_VAR/" -e "s/\${USERNAME}/$USERNAME/" -e "s/\${URL}/'$url'/" template > $filename.js
done
sed: -e expression #3, char 18: unknown option to `s'
sed: -e expression #3, char 18: unknown option to `s'
sed: -e expression #3, char 18: unknown option to `s'
sed: -e expression #3, char 18: unknown option to `s'
sample value of url is URL:https://example.com/app/index.html
EDIT FOR CLARIFICATION
data.txt
USERNAME_VAR:input_username
USERNAME:user01
PASSWORD_VAR:input_password
PASSWORD:password1
SUBMIT:submit
AUTH:cas
URL:https://example.com/app/calander.html
FILE:app_calander
URL:https://example.com/app/contacts.html
FILE:app_contacts
URL:https://example.com/app/search.html
FILE:app_search
URL:https://example.com/app/index.html
FILE:app_index
template
${USERNAME_VAR} = ${USERNAME}
${SUBMIT} IS TRUE
${PASSWORD_VAR} = ${PASSWORD}
${AUTH} = AUTH IS
URL TO HIT IS ${URL}
inject.sh
#!/bin/bash
USERNAME_VAR=($(grep -o 'USERNAME_VAR.*' data.txt | cut -f2- -d':'))
USERNAME=($(grep -o 'USERNAME.*' data.txt | grep -v 'VAR.*' | cut -f2- -d':'))
echo $USERNAME_VAR
echo $USERNAME
array_URL=($(grep -o 'URL.*' data.txt | cut -f2- -d':'))
array_FILE=($(grep -o 'FILE.*' data.txt | cut -f2- -d':'))
for i in "${!array_FILE[#]}"; do
#printf "%s\t%s\n" "$i" "${array_FILE[$i]}"
FILENAME="${array_FILE[$i]}"
URL="${array_URL[$i]}"
echo $URL
sed -e "s/\${URL}/$URL/" -e "s/\${USERNAME_VAR}/$USERNAME_VAR/" -e "s/\${USERNAME}/$USERNAME/" template > $FILENAME.js
done

Answer 1

Continuing from the comment, you could do something like:
for i in "${!array_FILE[#]}"; do
#printf "%s\t%s\n" "$i" "${array_FILE[$i]}"
filename="${array_FILE[$i]}"
url="${array_URL[$i]}"
sed -e "s#\${USERNAME_VAR}#$USERNAME_VAR#" \
-e "s#\${USERNAME}#$USERNAME#" \
-e "s#\${URL}#$url#" template > $filename.js
done

Answer 2

The answer to the first question is staring right at you: "${array_FILE[$i]}" is obviously different from "array_FILE[$i]"
To understand the "REAL ISSUE", just look at the error messages. They are telling you the problem is with the third sed expression, which assumes that $url does not have a "/" in it.
Unless you are certain that $USERNAME, $USERNAME_VAR and $url do not have "/" in them, then those sed commands will not work in the way you seem to expect.