Hi, 

@ is a special caracter, so, in order to get it working you must 'escape' it.

I've tried directly on the genio formula, and its working as expected:

Edit: Please note that this solution is only viable when working on interface level, with default formulas. Server formulas will not cope with this, so go with Maksym solution if that's that case.

Regards,

To be safer, create in Genio a function that does string formatting. The '@' character in MVC projects will give problems in JavaScript of this formula.

Implementations
CSharp:
return "@" + teamsName + ".com";

JavaScript:
return '@' + teamsName + '.com';

T-SQL:
RETURN '@' + @teamsName + '.com';

Then you can use this function in the formula

Note: Choose the type of formula depending on what is most appropriate for you.