Is there a limit to the number of inventory items that can be updated?

[Scott Lawson]

When using the Updating Inventory API call for both the v2 and v3 APIs, I get the message "Not a valid JSON string" for listings that have a lot of inventory items (i.e 800, 1200 etc).

I've tried it with smaller inventory amounts and it works fine. 

I've literally just tried reading and posting back the inventory JSON without making any changes to ensure it's a valid JSON object. Doing this works on listings with smaller inventory counts, so it makes me think there's a limit.

Is there a limit on the number of items? Or is it based on the size of the payload? And is there any way around this?