`step` required when requesting specific `param`s

[observingClouds]

What happened?

Request of param 49 fails, while it succeeds for other quantities.

I had hoped that apart from changing the param, requests for different quantities remain the same.

What are the steps to reproduce the bug?

The following request fails:

from polytope.api import Client
c = Client()
request = {
    'class': 'd1',
    'dataset': 'on-demand-extremes-dt',
    'expver': '0099',
    'stream': 'oper',
    'date': '20260405',
    'time': '0',
    'type': 'fc',
    'levtype': 'sfc',
    'georef': 'u3x2rb',
    'param': '49',
}
c.retrieve('deode', request, 'failure.grb')

only when step is provided, the request succeeds:

request = {
    'class': 'd1',
    'dataset': 'on-demand-extremes-dt',
    'expver': '0099',
    'stream': 'oper',
    'date': '20260405',
    'time': '0',
    'type': 'fc',
    'levtype': 'sfc',
    'georef': 'u3x2rb',
    'param': '49',
    'step': '0-1',
}
c.retrieve('deode', request, 'success.grb')

Version

0.7.6

Platform (OS and architecture)

Linux ac6-102.bullx 4.18.0-553.105.1.el8_10.x86_64 #1 SMP Sat Feb 7 00:49:44 EST 2026 x86_64 x86_64 x86_64 GNU/Linux

Relevant log output

Accompanying data

No response

Organisation

@dmi