Add hyperlink to email using custom action

Hi everyone
Not a developer, but trying and learning.
A business user in my app can add a customer user by adding their email and name. I’d like to be able to then send an email to that customer to download the app from either the Appstore or Google Play. I keep getting an JSON body error when typing in the code so I’m not sure what I’m doing wrong.

Also, has anyone had an experience with the field to input the JSON code where text gets wiped away? My cursor also jumps all over the place - it’s a real headache. I’ve had to write out the code in word then paste it into the field, and even then things don’t paste correctly and when editing, text disappears.

Screenshot attached of the code. Items in bold are magic text.

Thanks in advance!