Date field doesn't work for Expiration Date

Which field it's supposed to be? Expiration Date field must contain separate fields for month and year and a lot of time month is shown in letters (default Date field) e.g. March/2018. Anyway, there is no infos which field is supposed to be used in readme or install docu. Selecting Number field is just one field with commas, etc.

Notice: Undefined index: expiration_date in authorizenetwebform_handle() (line 342 of /var/www/example.com/htdocs/sites/all/modules/authorizenetwebform/authorizenetwebform.module).

Error response from Authorize.net: <pre>Array ( [0] => 3 [1] => 2 [2] => 33 [3] => Expiration date is required. [4] => [5] => P [6] => 0 [7] => [8] => [9] => 1.00 [10] => CC [11] => auth_only [12] => [13] => first name [14] => last name [15] => [16] => [17] => [18] => [19] => [20] => [21] => [22] => [23] => [24] => [25] => [26] => [27] => [28] => [29] => [30] => [31] => [32] => [33] => [34] => [35] => [36] => [37] => ECC33A11F79AAF6FC4A7503222A38A50 [38] => [39] => [40] => [41] => [42] => [43] => [44] => [45] => [46] => [47] => [48] => [49] => [50] => XXXX1111 [51] => Visa [52] => [53] => [54] => [55] => [56] => [57] => [58] => [59] => [60] => [61] => [62] => [63] => [64] => [65] => [66] => [67] => [68] => ) </pre>

I'm testing on Sandbox.