Double Complete Order request

After successfully completing the purchase at PayPal, the purchaser is returned to the website Checkout page, which requires the buyer to enter their UN & PW as well as RE-select the T & C AND rRE-select the Complete Order button. Why?
How can I prevent that from happening?

It’s confusing to me and probably both suspicious and confusing to the the Buyer.
If I complete the fields and comply with the instructions> Complete Order, I stay on the Checkout page, but now I’m logged in and it displays the Order Details identical to an E-mail that is received, containing the Click Here hyperlink which takes the person to the Item Page ie. in this case an OnLine Course
Can we remove that confusing intermediary step, where they are directed to login with out any explanation, and Complete Order, again?

Later, I’ll generate and redirect to a Welcome Page with a hyperlink to the Login.

Also, are you the ones generating the various confirmation E-mails? If so, where are you pulling the informational copy “We’re excited to hear about your project! Ready to begin? Click Here to get started.” from?

Thanks for your time,
Miguel