Based on what you mentioned, if the owner of
B4XUIKit has provided the following with the purchase of the library:
- Future design updates (lifetime free updates).
- Source code of the B4A library.
- JAR + XML files.
This means that the source code of
B4XUIKit is included with the purchase, giving you the freedom to edit it and integrate it into your project. If that’s the case, you can include the
B4XUIKit source code in your project and sell it without issues, as long as you comply with the terms of use for the library.
It’s important to note that if it’s a collection of example source code (and not just a runtime library), then you should be able to use and modify that code in your project as long as it doesn't violate any restrictions in the license that accompanies the code. Therefore, you can include this source code in your project and sell it, as you have access to the code and the freedom to modify it.
However, it’s always a good idea to review the specific terms of the license and, if in doubt, contact the author to ensure there are no additional restrictions on distributing that code, especially in commercial projects.
In summary, if you have access to the source code and the license allows it, you can include it in your project and sell it without issues.