pay button disappeared after upgrading membership

Hi there,

I'm new to Membership and this forum and installed membership 3.4.6.1 at first and the pay button appeared nicely. But when I upgraded membership to version 3.5 the pay button didn't show in the 'sign up for' pop up window. I'm using pronamic iDEAL as gateway.
How can I make the 'pay' button appear again in version 3.5?