Would it not be easier to create the form in paypal and then use this code?
If you only have a few variables this would be best. Create the form as you would normally for a button via merchant services and just add more details.
Add text fields (limited to 2 I think) but you can get more in by using a pull down bar.
If you can’t get this to work you can get the contact 7 form to send you to paypal once your done. It will email you the info but it won’t pass it over.
As per https://spynboxe.com/adding-paypal-to-contact-form-7/