Hi @bencevilagi,
I will think about adding it to the plugin. Meanwhile, you can do it with a small JavaScript code. You can use any tool for adding custom JS code, but I would suggest using our another small Custom CSS, JS & PHP plugin for that. After installing, you will need to go to “Tools > Custom CSS, JS & PHP”, locate “JS: front-end” option there, set position to “Load in footer” and set “JS code” option to:
document.querySelector( "#billing_eu_vat_number" ).addEventListener( "keypress", function( evt ) {
if ( evt.which < 48 || evt.which > 57 ) {
evt.preventDefault();
}
} );
Please let me know if it’s not working as expected or if you have any questions.