Unexpected error : Invalid domain name, underscore not allowed

[mildis]

Using OctoDNS, I try to create entry
1.0.0.127.in-addr._spf.example.com

but if fails with

  File "/usr/local/lib/python3.13/site-packages/ovh/client.py", line 535, in call
    raise BadParametersError(json_result.get("message"), response=result)
ovh.exceptions.BadParametersError: Invalid domain name, underscore not allowed 

I understand this is a feedback message from the OVH API but as there is already a TXT RR for _spf.example.com I'd like to update to v=spf1 exists:%{ir}.%{v}._spf.example.com -all

I don't know what is wrong with this entry.