TypeError: Illegal invocation

Your datatype is not JSON, it’s a FormData. And for jQuery to send a FormData, it needs…
$.ajax({
    type: "POST",
    url: 'signin2.php',
    data: formData,
    processData: false, //add this
    contentType: false, //and this
})

Similar codes

1 vote423 views1 answer
Html how to make text not bold
Html
2 votes261 views2 answers
How to link to another part of the same page
Html
0 vote328 views1 answer
Cursive text html
Html
40 votes322 views4 answers
Using svg in html
Html
0 vote322 views1 answer
Wikipedia api url
Html
0 vote352 views1 answer
Vue-date-pick
Html
3 votes341 views1 answer
Html non selectable option
Html
0 vote359 views1 answer
Make dictionary english html
Html
0 vote325 views1 answer
How to stop html audio
Html
5 votes400 views1 answer
How to center html heading
Html