Why me? I have experience in LearnDash, my main area of experience is elearning, from LMS development & management to online course development.
I am probably asking for more cost than others, but this is a guarantee to fulfill your requirements.
What I will do is configure PayPal for you, I think there is a missing thing on your system, I will add the missing part, configure PayPal payment gateway for you, not only this, but in order to make it work fine, there are a few other things that need to be done, like setting the cost to take the course, set any discounts if necessary.
There is a couple of bugs also in LeanDash and WordPress based LMS's in general, I can fix those as well for you to make the website work well for you.
Kindly review my humble profile then initiate a chat with me to discuss project details.
Thanks and best regards,