want to put size validation in file upload

Currently, this isn’t a built-in option, but you can add a little code snippet to check the size when the user clicks submit. Here’s the code snippet:
https://formidablepro.com/knowledgebase/frm_validate_field_entry/#kb-limit-uploaded-file-size

You can add custom code like this to your theme functions.php or a new plugin. If you have additional questions about this, please post in our Help Desk for support:
https://formidablepro.com/help-topics/

First of all thank you your solutions given is worked f9 but there is a litte bit problem it validates after the fully completed file upload. so problem is that i have putted 64MB Maximum file when user upload 70MB file than it completed upload 70MB after it give. i have to validate before the file upload. so when upload it immideatly check and validate and reply. so help me in that. Thank.. YOu.. ??

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