503 response on a single request (synonyms for Leptochilus aterrimus)

Hi everybody,

I’m using the API in a small application I wrote in python and a funny error is popping up.
I procedurally ask the API for a series of names collected

This is the python code that builds the API request
taxa.links: is a list of links that I get from GBIF
file_info is just a class to manage stuff saved on my hard disk
Request Handler is a wrapper of the requests class in python
everything can be found in this repository: https://github.com/Pella86/ScrapeTax

    url = taxa.links[0] + "/synonyms"
    filename = file_info.cache_filename(f"{taxa.genus}_{taxa.specie}_synonym")
    
    req = RequestsHandler.Request(url, filename)
    req.load()

And only for this particular request I get a 503 status code. I tried to look in the response header and it tells me to wait 5 seconds, but… I tried it different times, and it still gives me a 503 status code
https://api.gbif.org/v1/species/5037930/synonyms

the funny thing is that if I paste it in the browser the request works and gives me the synonyms.
Do you have any idea what might cause this?