POST tool returning error

Im getting an error when using the post tool to a server that requires the Accept header:

"The 'Accept header must be modified using the appropriate property or method.
Parameter name: name"

The API setup was working properly before and this error started when I think the API started using the header on their side. Either way, its a coding issue on our end.

This is one Im calling: Investec programable banking, SA PB Account Information : Transfer Multiple v2

Its probably too dificult to setup on your end so happy to help with this where needed.