Interesting query and equally importantly, interesting debate among fellow professionals! That's beauty of this forum! It sometimes forces professionals to think beyond obvious.
On the issue under discussion here, I tend to agree with views of Ms. Shilpi JainJi, though views of Shri Katuri SethiJi forced me to think beyond the obvious. I thank both of them, the querust and other contributors for this experience.
And in my humble submission, requirements under section 76 needs to be interpreted covering a situation where a person, who has collected from any other person any amount as representing the tax under the Act, does not pay the same to Govt. on the ground that concerned supply is not taxable under law.
It is worth noting that all other provisions (such as section 73, 74 and so on) deals with recovery of taxes and penalty for not paying the same under various situations.
But what happens when underlying supply is claimed / held as not taxable thereby 'amount representing tax' though collected but it does not fulfils characteristc of 'taxes' in law. Hence, Section 76 covers a situation where person collects an 'amount representing taxes' but does not deposit it to Govt. by claiming non-taxable supply thereby trying to avoid regular recovery & penal provisions of law.
For the situation under discussion here (where taxability of supply per se is not under dispute), in my view, Notification No. 66/2017 – Central Tax "officially" allows postponement of paying 'taxes so collected' to the point of the time of supply as specified in clause (a) of sub-section (2) of section 12 of the CGST Act, 2017.
Once there is no delay in paying the 'taxes so collected', there is no interest liability in given situation in my view.
Kindly treat all my views as strictly personal and not as a professional advice / suggestion.