Can't create a form within a shared folder

I have been shared a folder by a company who has a large account with you and have already upgraded to create many forms but when I try to create a form it's asking me to upgrade.  I want to create the form within the shared folder, not upgrade my own account.

I have clicked on the shared folder, so it is highlighted, selected 'create form' and it still isn't allowing me to do it.

What do I need to do?

Please note that sub-users can only edit the form and view submissions of the form shared to them. Your account and their account are different, so you need to upgrade as well if you want to create more forms.

They can create a folder and share it with you. Once the folder is shared with you, you can move the forms from your account to the shared folder. It is like you are transferring forms from your account to their account.