Using a package code to book through a Direct Schedule Link

I have a few clients that want a regular slot every week and so I have created a direct schedule link for them so they can book their slot without anyone else jumping in and booking it.  I have a client who has purchased a block booking package.  When she has paid for the package, she is given a code.  However, when she goes into her direct schedule link to book her lessons, her code is not accepted in the payment section.  Can anyone help me with this?