[Python] How do I fix a traceback error in a CS50 Credit Pset in Python?

Been working on a Credit Pset in python. Decided to use regular expressions. Everything was fine before I got to the Lunh's algorithm part. Now I get traceback errors and don't know what to do with them.

Here is the code:

import re


def main():

card = int(input("Card number: "))
validate(card)


def validate(card):
if re.search(r"^(34|37)\d{13}$", str(card)):
print("AMEX\n")
elif re.search(r"^(51|52|53|54|55)\d{14}$", str(card)):
print("MASTERCARD\n")
elif re.search(r"^[4](\d{12}|\d{15})$", str(card)):
print("VISA\n")

sum = 0
productSum = 0

# Reversing the str with [::-1]
for i in range(len(card[::-1])):
if i % 2 == 0:
sum += int(card[::-1]) * 2

if sum > 9:
# Using modulus operator to get the second digit of a product (second digit is the remainder)
n = sum % 10
# Using integer division to get the first digit of a product (disregarding the remainder)
m = sum // 10
productSum = n + m

sum += productSum

for j in range(len(card[::-1])):
if j % 2 == 0:
sum += int(card[::-1][j])

if sum % 10 != 0:
print("INVALID\n")


if __name__ == "__main__":
main()


The check50 errors are the same for every expected "INVALID" output:

Traceback (most recent call last):
File "/tmp/tmph_wbo0m4/test9/credit.py", line 43, in <module>
main()
File "/tmp/tmph_wbo0m4/test9/credit.py", line 7, in main
validate(card)
File "/tmp/tmph_wbo0m4/test9/credit.py", line 21, in validate
...


The rubber duck only tells me that the problem is in validate() function. Thank you.

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