Set Caldera Forms Paypal express currency conditionally with a dropdown select field.

cf-set-custom-currency.php

<?php
add_filter( 'cf_paypal_request', function(  $request, $process, $form ) {
  
    //SET THE FORM ID AND THE FIELD ID ( DROPDOWN FIELD WITH CURRENCY OPTIONS )
    $form_id = 'CF5a5e8452c6f82';
    $field_id = 'fld_8085538';

    if ( $form['ID'] === $form_id ) {
        if ( $process['data'][$field_id] === 'USD' ) {
            $request[ 'PAYMENTREQUEST_0_CURRENCYCODE' ] = 'USD';
        } else if ( $process['data'][$field_id] === 'EUR' ) {
            $request[ 'PAYMENTREQUEST_0_CURRENCYCODE' ] = 'EUR';
        } else if ( $process['data'][$field_id] === 'CAD' ) {
            $request[ 'PAYMENTREQUEST_0_CURRENCYCODE' ] = 'CAD';
        }
    }

    return $request;
}, 10, 3);