Looking at the source code - vyos-1x/data/templates/accel-ppp/config_chap_secrets_radius.j2 at current · vyos/vyos-1x · GitHub
it appears that the cli priority option is being emitted to accel‑ppp as weight=N
{% if options.priority is vyos_defined %}
{% set _server_cfg = _server_cfg + ",weight=" + options.priority %}
{% endif %}