Then post what you want to accomplish and your best try (as indicated as a requirement in the FAQ) so maybe some users can have a look at it and try to help.
You missed the part of @Mark’s message about posting your best try. Without that, you are just asking others to do your work for you. And that is against our rules.
Aside from that, if you want to develop your own themes and email templates, you should know that they’re written in HTML and Liquid templating language.
Here’s some additional resources to get you started:
For the complete list of available variables, you check out the Plain theme or any of the other themes that come installed by default. All the variables are used there.
Together with the resources listed, that’s about everything you need to create a custom theme or email template. Other forum members will be pleased to help you fix any problems you face along the way.
This Forum is one of two primary sources of help on how to use Manager accounting software. The other is a set of Guides
There is no other support. The programmer @lubos participates actively and responds through this forum as do the moderators such as @Ealfardan and other users such as I that have an interest in learning and helping others. You will notice that often responses related to customizations, themes and apis are referred to maybe needing to hire a programmer to help you as this is not within the services provided by Manager. If you have payment problems or similar you could use the private message service of this forum to @Lubos.