Member Signal can only work with Wild Apricot accounts on paid billing plans. It is an intentional limitation to protect our system from spammers and thus make service more reliable for our customers.
You can still explore your FREE or TRIAL Wild Apricot account to Member Signal. However, the system will not allow you to send messages.
If you want to switch Member Signal to a different Wild Apricot account, then you can do it by updating an API key in Wild Apricot integration settings.