Hi @Fashionhero!
I see that you’ve reached out to our Support team and they responded to you. For anyone else who finds this, here’s what our team had to say:
An issue is occurring here due to the value being provided in the "Base" field.
Whenever you see a field with a double-headed arrow on the right in the Zap editor, this means that the connected app requires a specific ID value.
When you click in this field, we will make a call to that app to ask them what values they expect. This will be shown in the drop-down menu that appears.
The value in bold on the first row is the human-readable text, this is what you'll see when you're using the app. The value on the second line is the ID value, which is automatically created in the background by the connected app.
(view larger)
It is this ID value which is required in order for the app to correctly parse the data.
At this time, the GitHub integration doesn't support uploading a file. So I'm not sure that you'll be able to achieve what you're after using the GitHub integration.
We do have an open feature request to add a "Create File" action, and whilst I don't have an ETA on when this might happen I have added you as an interested user. This way, we can notify you when this feature is implemented.
You might be able to achieve what you're after by using a custom webhook. Webhooks allow you to create your own custom requests to send/receive data in a Zap. You can learn more about webhooks here.
Just to be upfront, Webhooks by Zapier is considered an advanced feature, so our support for it is more limited. Not because we don't want to help, but because APIs can be so different and each request can be so unique. This makes it hard for us to know why the request may be receiving errors or not working as expected.
For anything that I may not be able to answer, the best place to ask for help may actually be stackoverflow.com. Tag your question with a “Zapier” tag, and usually, there will be folks who’d be willing to help you out. You can see all questions that have already been asked here: http://stackoverflow.com/questions/tagged/zapier
I hope that helps and please let me know if I can assist with anything else.