I have found a work around that works for me.
Simply enclose the personalization token in “”. The value is transferred with the “”, but I can live with that compared to giving my users a 404.
Change the link in the email from:
…/link?email={{contact.email}}&accountname={{contact.freetrialaccount}}
To
…/link?email={{contact.email}}&accountname="{{contact.freetrialaccount}}"
The account name is then filled with the content of the custom field freerialaccount enclosed in “”.
So instead of having this in our application:
account name
Then we get
“account name”
Not ideal, but much, much better than 404 and a lost trial account.