Under which section should I pay IGST - Service delivered in India for Foreign entity

Hello sirs,

I work with an international company for whom I deliver trainings in India, the payment comes from the international entity.

Till now I was filing under section 6A (Export Invoice) with payment of IGST.

However, I got an notice today "Non-transmission of invoices due to negative balance" stating that the validation failed and the details did not get transmitted to ICEGATE server. I am NOT claiming any credit for this.

Am I doing the right thing? kindly Clarify.

Raju Madhavan