Read non-unique grid format

Hello everyone,
can someone explain to me when I got this error, please?

grdcontour [ERROR]: Cannot determine if a native 4-byte grid is float or int without more information.
grdcontour [ERROR]: You must append =bf (float) or =bi (integer) to avoid this situation.
grdcontour (gmtapi_import_grid): Non-unique grid format [data/bmg2023fqis/bmg2023fqis.b]

I use pygmt v0.8.0 and GMT v6.4.0 and this is my script in pygmt

grd_eta = ‘data/bmg2023fqis/bmg2023fqis.b’

So, where should I put =bf or =bi in the script?

Well, do you know what kind of grid you have? That message can mean one of two things:

  1. Your grid is a native GMT binary grid using 4-byte elements that can either be ints or floats. There is no info in the header to tell us the difference, hence the message.
  2. The grid is another format that GMT does not understand but thought it did.

Depending on what you know about your grid you either append =bi or =bf to the filename or you pass it via GDAL by appending =gd.