Hi Oliver. You can set up a form that will collect all the relevant information, and then allow the fields to be populated dynamically. Then, with the link, you can populate those fields. Here is a description of how that works:
I put together a form that showcases this functionality. Imagine I sent you this email:
Hi Oliver. Thank you for allowing us to work with your on your design project. As discussed, here is a customized invoice link you can use for payment. Once this invoice is paid, we can move on to phase II of the project! If you have any questions, please let us know.
If you click that link, you will be redirected to the form on my site which will have all those details prefilled. The fields are marked ‘read only’ so they can’t be edited easily in the browser. The only thing required to submit the form is the credit card information. You can use a test credit card, as noted at the top of the form, to submit the form. No funds will be exchanged, as that payment add-on is in test mode.
The information could of course be edited in the URL/browser, and I actually suggest you try that (change the email address for sure), to see what the receipt looks like when it is sent to you after completing the form.
If this will work for you, let me know. I can give you more information about what is required to accomplish this if you need help. Thank you.