warning: regexp escape sequence "' is not a known regexp operator

Hello and sorry to bother you but I`m trying to run this script and for some reason I can`t because of this error:
$ bash task1.sh accounts.csv awk: cmd. line:31: warning: regexp escape sequence "' is not a known regexp operator

To me the line it`s "empty"
This is the script, if this is not where it should be, please forgive me and let me know where should I ask this question.

Code:#!/bin/bash

# Exit if path to accounts.csv file not provided as argument
if [ $# -lt 1 ]
then
echo "Usage: ./task1.sh /path/to/accounts.csv"
exit 0
fi

file=$1

# Exit if provided file doesn't exist
if [ ! -f $file ]
then
echo "File $file doesn't exist"
exit 1
fi

# Extract directory from file
path=$(dirname $file)

# Processing csv file with awk
awk '
# Set Field Separator and Output Field Separators
BEGIN { FS=","; OFS=",";}

# Skip first row, as it contains only column names
NR == 1 {
print
}

# First pass through file to check for uniqueness of emails
NR == FNR {
# 3rd field contains name
# splitting name to first name and last name
split($3, name, / /)
email = substr(name[1], 1, 1) name[2]
email = tolower(email)
++counter[email]
}

# Second pass through file, skipping first line
NR > FNR && FNR != 1{

# Create an array from fields as the default FS processes
# quoted commas incorrectly

j=0
inside_quotes=0
for(i=1;i<=NF;i++) {
# Opening quote, save to new field,
# set inside_quotes to true
if($i ~ /^\"/) {
inside_quotes=1
j++
fields[j] = $i
}
# Closing quote, append to last field, set inside_quote to false
else if($i ~ /\"$/) {
inside_quotes=0
fields[j] = fields[j] OFS $i
}
# middle of quoted text, append to last field
else if (inside_quotes==1) {
fields[j] = fields[j] OFS $i
}
# outside of quotes, save to new field
else {
j++
fields[j] = $i
}
}
# fields[3] contains name
# Split name by space
split(fields[3], name, / /)
# Change the first character to uppercase, all other characters to lower case
name[1] = toupper(substr(name[1], 1, 1)) tolower(substr(name[1], 2))
name[2] = toupper(substr(name[2], 1, 1)) tolower(substr(name[2], 2))
# Change the 3rd field to new value
fields[3] = name[1] " " name[2]

# email format: flast_name@abc.com
email = substr(name[1], 1, 1) name[2]
email = tolower(email)

# if the email is not unique, append location id
if (counter[email] > 1) email=email fields[2]
fields[5] = email "@abc.com"

# Set new values for all 6 columns
NF=6
for(i=1;i<=NF;i++) $i=fields[i]
print
}
' $file $file > $path/accounts_new.csv