Hello Chris
In order for PPP authentication to use the PAP password that you have configured, it is necessary to specify the method by which AAA will occur for PPP. By default, the local database is used, that is the credentials created with the username my_username password my_password command. If that has not been set, then authentication cannot take place. Note that what you have configured about is the “calling” side. The other side must be configured with this username and password.
Cisco has excellent documentation on how to set up the PAP connection for PPP. Take a look at their step by step instructions and their examples, and I believe you should be able to troubleshoot the issue.
Let us know how it goes! I hope this has been helpful!
Laz