I want to create a subdomain, i think

I want to create a subdomain…I think.

I own 2 domains that are on Google Domains. One is my personal one, and one is a business domain. Both have a forward entry to send traffic to a main page. One personal and one business.

For sake of discussion, let’s call the business one mydomain.com. the personal one isn’t relevant here. I want my business domain to be able to take facebook.mydomain.com and direct traffic to my Facebook Marketplace page, I have the link. Since I already have a forward request that takes the mydomain.com traffic and sends to my page, I am not able to setup another forward for facebook.mydomain.com.

How can I do this?

BTW, I am hosting my personal domain on WordPress running on my Synology nas.

So your mydomain.com should just have an A or CNAME pointing to your homes IP, rather than actually being a forwarder. To use no subdomain (as in just mydomain.com) you use @ for the subdomain when you are entering it in DNS manager