That header indicates the request response/reply can be JSON, don’t think it makes a difference here 
(it’s JSON already)
i added the header anyway just in case and it gave the same error…
I also added the same api to a new hosting OrangeHost which is popular around here and it gave the same exact error…
This API was working perfectly before and i’m 100% sure this is a bug in the software and i wish Wappler would give it some attention …
You need to progress the diagnostics with Beeceptor so the Wappler team has additional knowledge about what’s happening.
If you don’t do that, this will be a low priority case (unfortunately).
I’m just trying to facilitate things moving forward 
However, I understand if feels a bit complicated. I also lack the time to assist further. Hope you get the problem solved
P.S: Wappler team comes back to work tomorrow (Monday), maybe they’ll reply to you by then
I give up I been at it for days…I guess I’ll have to recreate in regular php