match.arg(method) Error : stop("'arg' must be NULL or a character vector")

Theres a concept in computer science called a 'code smell' Wikipedia.
This sort of mixing of tidyverse and base programming is a strong code smell to me.
if you are filtering on KTE_GI, you don't need to mention it in every filter criteria, B_COEFF is right there to be interpreted in the context of KTE_GI without need of $.

I would encourage you to come up with a different approach to implementing your calculator. it seems to me you need a look up table to interpret FRANCH codes, probably your code could be simplified to a straightforward join followed by filter.

For additional / specific support I would ask for a proper reprex, with representative data to be shared.

[FAQ: How to do a minimal reproducible example ( reprex ) for beginners]