Form cannot be filled through mobile browser, but works fine with Laptop browser

I am losing clients because of this, kindly fix this issue or help me fix this issue ASAP

If you have an error that you want fixed by Squarespace then you'll have to contact Squarespace Support:

https://support.squarespace.com/hc/en-us/requests/new#choose-topic

Try adding this to Website > Website Tools > Code Injection > Header

<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0,user-scalable=0"/>
<style>
@media screen and (max-width:640px) {
.sqs-modal-lightbox-content .lightbox-inner .lightbox-content {
   padding-bottom: 250px !important;
  }
}
</style>