[resolution] BO/Livraison/References/ "Free shipping from" calculation based on TTC. HT Besoin

[chaudhary]

I work on the website of a client who sells musical instruments and thus only to professionals.

Configuration: ps 1.7.6.2, theme payant wharehouse purchased on theme forest).
The website is https://mymusicdistribution.fr/.
The shop is set up as a B2B with HT pricing displayed.

My issue is with the calculation of port fees offered starting at 500€ of purchase via the transporters/preferences/free shipping starting at..."
PS computes whether or not to apply the FDP gratuity to the TTC amount. After that, I need it to be calculated on the total amount of HT products. Because we have some professional clients who do not pay tva and others who do (people in the community do not pay tva).
So, if I pay tva, I have FDP offers starting at 417€ HT (so it's 500 ttc with 20% tva), which is not good, and if I don't pay tva because I have an intracom number, I have FDP offers starting at 500€ HT (and thus ttc because there is no tva applicable).

I discovered an intriguing override that does not work: https://www.team-ever.com/problemes-et-resolutions-sous-prestashop/#comment-85039
This override proposes calculating discounts on the HT rather than the TTC, but I believe the class that manages the port fees starting at x€ is different.

Could you please tell me which class manages this and if you have a code to apply as an override?

Thank you in advance for your responses.