Where is the power to levy GST derived from?

Article 246A of the Constitution, which was introduced by the Constitution (101st Amendment) Act, 2016 confers concurrent powers to both, Parliament and State Legislatures to make laws with respect to GST i. e. central tax (CGST) and state tax (SGST) or union territory tax (UTGST). However, clause 2 of Article 246A read with Article 269A provides exclusive power to the Parliament to legislate with respect to inter-State trade or commerce i.e. integrated tax (IGST).