Custom Power up t.attach function giving "Uncaught Error: User lacks write permission on card."

Question

I'm creating a custom power up which requires me to use card buttons to attach a link to the card, however I keep getting the above error whenever I call t.attach function. I authorized the user with read and write permissions using the following url:

"https://trello.com/1/authorize?expiration=never&name=[App-name]&scope=read,write&key=[api-key]&callback_method=fragment&return_url=https%3A%2F%2F' + window.location.host + '%2Fauth-success"

After much debugging, I found that "t.memberCanWriteToModel('card')" returns true when the user is authorized. After the authorization window closes and the flow returns to the default app, the function returns false.

Trello User · Accepted Answer

I figured it out. The page that was calling the t.attach method was loaded using window.location instead of t.popup method