Workflow API data gets corrupted/scrambled/wrongly formatted

I have an external server from which I send HTTP requests to Bubble to activate a backend workflow, which in turn activates a workflow on a list of things:

notice how I convert values to numbers, because in the following JSON the numbers are sent as strings.
Here is the JSON body of the request I send, as properly received by Bubble when setting up the workflow with ‘/initialize’:

(there’s only closing brackets after the image)

For some reason when running the ‘run an api on a list’ workflow, this happens to the list of values:

Why does this happen?