Some countries need a specific number format. Always select the country in the Schedule call window first, then enter the number without spaces, dots or dashes.
Mexico: enter the 10-digit number (area code + number). Don't add 1, 044 or 045; these prefixes are no longer used.
Argentina: for mobile phones, add 9 before the area code.
Brazil: include the 2-digit area code (DDD) before the number (mobile numbers have 9 digits).