Server validations has a Regular Expression type validation you can apply.
There is server side code you have to add for reCaptcha v3 that you are probably missing.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.