When I tried to insert a Mexican number, I am unable to input the international code for the number. For example,+52 1 8133233233 does not work but without the , +52 8133233233 works. Why does this happen?
This limitation exists because of Mexico's new policy.
You can submit the phone number without  and Facebook will automatically add back  later to your number.
For your reference:
"As of August 3, 2019, phone numbers in Mexico have ten digits. The new national number was formed by appending the area codes to the local number . All phone numbers should be dialed in a ten-digit format, even for local calls."