oh good god i spent ages on this and ive just seen the error.
add_filter('acf/upload_prefilter/key=field_627a6567e2078', 'field_name_upload_prefilter');
function field_nameupload_prefilter($errors) {
one has a gap in the name …. the other doesnt
And of course it exists its a function name created. Full on developer brain meltdown today
