I am happy to believe I am approaching this the wrong way. I followed the tutorial you have over here:
Your own Donate button seems to do the job I also want to do. When people click it, they get an option to either pay with an ordinary credit card, or else to pay by PayPal.
As against that, the Free Tools that I found do not help me.
Firstly, the Donate button in those Tools does not give people the option of paying with ordinary credit cards. And secondly, the PayPal Business account I have allows people to remain on my site to pay me rather than leaving to go to over to PayPal.
Have I downloaded and installed the wrong tools? I found freebies for Skype, for Google, and for PayPal.
I attach the two files I have created, using the above Webassist tutorial I found earlier.