The third input to the fints function is a cell array of strings that can be valid MATLAB identifiers. That is, the strings cannot start with numbers and can only contain letters, numbers, and the underscore. As a workaround, you could do this
dataNamesInput = cellfun(@num2str,num2cell(xDataNumbers(:)),'uniformoutput',false);
dataNamesInput = cellfun(@(s)['x',s],dataNamesInput,'uniformoutput',false);
dataNamesInput = regexprep(dataNamesInput,'\.','_');
and use dataNamesInput as the third input. Someone may suggest using the genvarnames function, but it will replace periods with '0x2'. You may prefer that. In any case, you'll still need the first line of code above that converts numeric array to cell of strings.