I am tasked with a workflow on SharePoint Online that includes uploading an image to a different Site Collection and changing the Site Collection's logo.
Is there a way to do using a Call HTTP Web Service action since i don't see a Nintex Workflow action to accomplish the task?
This is a great question. While I have not seen an API specific to that, I'd imagine it may be similar to the on-prem call.
Take a look at this and see if it gets you anywhere Programmatically change subsite logo