Use multiple PHP-FPM versions using FastCGI on same Debian/Apache server

I would like to use multiple PHP-FPM versions using FastCGI on same Debian/Apache server. Using:

• Debian v9.12,
• Apache v2.4.25,
• php5.6-fpm,
• php7.4-fpm,
• libapache2-mod-fcgid v1:2.3.9-1+b1,
• libapache2-mod-php5.6 v5.6.40-26+0~20200320.32+debian9~1.gbpec51cd,
• libapache2-mod-php7.4 v7.4.14-1+0~20210112.34+debian9~1.gbpaa175a.

I would like to use php5.6-fpm, php7.4-fpm on the same server.

The site should use PHP v5.6 by default and should use PHP v7.4 on php74.mysite.com subdomain.

I use the following Apache config files:

mysite.conf:

<IfModule mod_ssl.c>
<VirtualHost *:443>

DocumentRoot "/var/www/mysite.com/htdocs"
ServerName mysite.com:443
ServerAlias *.mysite.com:443 www.mysite.com:443

SecAuditEngine On
RewriteEngine On
SSLEngine on

LogLevel warn
ServerSignature Off


    <FilesMatch "\.php(/.*)$">
        SetHandler "proxy:unix:/var/run/php/php5.6-fpm.sock|fcgi://localhost/var/www/mysite.com/htdocs"
    </FilesMatch>
 
    <Proxy fcgi://localhost/var/www/mysite.com/htdocs enablereuse=on max=10>
        ProxySet connectiontimeout=3600 timeout=3600
    </Proxy>

    RewriteCond %{REQUEST_FILENAME} \.php$
    RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_URI} !-f
    RewriteRule (.*) - [H=text/html]
 

<Directory />
    Options FollowSymLinks
    AllowOverride None
</Directory>

<Directory /var/www/mysite.com/htdocs>
    Options Indexes FollowSymLinks MultiViews
    DirectoryIndex index.php
    AllowOverride None
    Require all granted
</Directory>

ErrorLog /var/www/mysite.com/log/error.log
CustomLog /var/www/mysite.com/log/access.log combined
CustomLog /var/www/mysite.com/log/ssl_request_log \
            "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"

</VirtualHost>                                  
</IfModule>

php74.mysite.conf:

<IfModule mod_ssl.c>

<VirtualHost *:443>

DocumentRoot "/var/www/php74.mysite.com/htdocs"
ServerName php74.mysite.com

SSLEngine on
SecAuditEngine On
RewriteEngine On
SSLProxyEngine on

LogLevel debug
LogLevel alert rewrite:trace8

ProxyPreserveHost On


<Directory /var/www/php74.mysite.com/htdocs>
    Options -Indexes +FollowSymLinks +MultiViews
    AllowOverride All
    Require all granted
</Directory>
    
<FilesMatch "\.php(/.*)$">
        SetHandler  "proxy:unix:/run/php/php7.4-fpm.sock|fcgi://localhost/var/www/php74.mysite.com/htdocs"
</FilesMatch>
<Proxy "fcgi://localhost/var/www/php74.mysite.com/htdocs" enablereuse=on max=10>
</Proxy>


<Directory /var/www/php74.mysite.com/htdocs>
    Options Indexes FollowSymLinks MultiViews
    AllowOverride None
    Require all granted
    DirectoryIndex index.php
</Directory>

    
ErrorLog /var/www/php74.mysite.com/log/error.log
CustomLog /var/www/php74.mysite.com/log/access.log combined


CustomLog /var/www/php74.mysite.com/log/ssl_request_log \
            "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"

</VirtualHost>                                  
</IfModule>

Uploaded a phpinfo.php to both site htdocs:

<?php

phpinfo();

?>

Unfortunately on php74.mysite.com displays:

PHP Version 5.6.40-26+0~20200320.32+debian9~1.gbpec51cd
...
Configuration File (php.ini) Path   /etc/php/5.6/fpm
Loaded Configuration File   /etc/php/5.6/fpm/php.ini

How can I force to use PHP v7.4 on php74.mysite.com?