Regex not working in code but works in tool:
\+?\(?([0-9]{2})\)?([ .-]?)([0-9]{4})\2([0-9]{4})
This regex is used in Custom Attribute in MVC application. Where it always invalidate the model. While it works accurately in online tools.
I am trying to validate phone number is this format: +(55) 7564 6242
You didn't specify the language, but from Attribute and MVC I'm guessing C#.
You have to escape your regex strings for the source code.
Original pattern
\+?\(?([0-9]{2})\)?([ .-]?)([0-9]{4})\2([0-9]{4})
Regular C# (or Java) String
string pattern = "\\+?\\(?([0-9]{2})\\)?([ .-]?)([0-9]{4})\\2([0-9]{4})"
C# verbatim (better for regex / hardcoded Windows paths)
string pattern = @"\+?\(?([0-9]{2})\)?([ .-]?)([0-9]{4})\2([0-9]{4})"
See C# String Literals for more info.
Without Escape
An unescaped string would result in a pattern that the regex engine just doesn't recognize (see output below), because \\ is special in your source language strings. It probably escapes it something like this
string pattern = "\+?\(?([0-9]{2})\)?([ .-]?)([0-9]{4})\2([0-9]{4})";
print(pattern);
would output (note the missing \\s)
+?(?([0-9]{2}))?([ .-]?)([0-9]{4})2([0-9]{4})