Oh man... I just searched for this. No idea it had been removed. What a nightmare. Please bring it back. 

Thank you @lgaertner So it seems we have to add this as raw JSON. I was trying to use the URL Encoded parameters which didn't work. I have looked at the API Explorer, it just wasn't clear were I put these parameters.Your method works. Thank youRob

Just thought I would write back and let you know that this worked for me. I used Create JSON Thank you again.

Thanks. I'll give that a try and let you know

Oh No. I've found the solution, my category ID was actually incorrect.Slightly embarrassing Sorry for wasting your time.Rob

@ChrisStephens That was my initial thought, so I pulled the API name out via the API (POSTMan) then copied and pasted in to Fusion. So just assumed I needed to escape the character. 

@ChrisStephens The updates are in the JSON object in the body of the POST request. e.g. {"name":"test","DE:Paramater Name":"123","DE:Paramater Name 2?":"456"} The name of the parameter here has a question mark. When I submit it, it then tells me it can't find the parameter with that name. 

Thank you for your reply. I'm actually using Fusion (I updated my question). However, I think I tried replacing the question mark with %3F and it didn't seem to work.Rob

@ChrisStephens Sorry, I missed your reply. Thank you. I hadn't seen the GET function, this is useful. I know this is a different question slightly... but is there such a function like isArray()? to tell whether the value returned from a multiselect is an array or not? Currently I use join() using an...

Thanks for looking into this @Doug_Den_Hoed__AtAppStore So, when I tried this as a calculated field on a custom form, this is how I had to implement it to work:REPLACE("test123","123","\u0000")   =>  "test"(Only a single \ symbol) Really useful to have these two codes. Thank you. Hopefully Workfront...