Haproxy error 413 paylod too large

I’m using haproxy as LB for rabbitmq management portal.
When I try to purge a queue in the UI, I get error 413 payload too large.
In this article https://bobcares.com/blog/413-request-entity-too-large-haproxy , the author talk about “http-request max-body-size” option, but if I try to add it, even frontend or backend, I get the error “http-request expected set-hdr […] passed max-body-size”.

I have already try with tune options, but nothing worked.
This are the options I used for testing purpose:
tune.bufsize 131072
tune.maxrewrite 32768
tune.http.cookielen 1024

How can I increase the http body size in haproxy?

I don’t think HAProxy will generate 413 responses without specific configuration… I’d advise you have a look through the access log from HAProxy. It should lead you to “who” is making the 413 response.