GST registration for transport business

if you only have an income which comes under RCM then registration is not mandatory.

can you please elaborate it

As per Notification No. 5/2017- Central Tax dated 19/06/2017, a person who is only engaged in making supplies of taxable goods/services, where the total tax on which is liable to be paid on reverse charge basis by the recipient as the category of persons exempted from obtaining registration under GST.
Thus, a GTA does not have to register under GST if he is exclusively transporting goods even if the turnover exceeds 20 lakhs as the total tax is required to be paid by the recipient under reverse charge basis.

thanks brother 👍👍