Regarding GHMC unapproved apartment

The approval of the competent authority which is generally known as NOC is a mandatory thing. If the builder knows that his land papers and other documents are in place, he will get it sooner or later so he may be not taking it seriously.

Generally, people book houses and NOC follows with time. But in some cases where there is some legal problem NOC is not given and the authority can even ask for the demolition of the building.

So you have to find the exact situation from the inner sources in builder's office or GHMC office.

Alternatively, you can pay some advance to the builder but tell him that the remaining money will be given only after NOC process.

You also find out whether registration of the property is allowed before NOC process in that area or not because this will force the builder for applying for NOC.

Please keep in touch with the other people also and go for collective wisdom rather struggling alone with the builder.

GHMC approval is a must if the area in which your apartment is being constructed.
If there is no approval GHME may ask you to pay hefty amounts up to a maximum of 100% of the value of the building. If we are not paying the fine they may come and bet the building collapsed also. recently buildings of some cine actors were being broken by the authorities. So we should not take any risk in that respect.
So I advise you to get the GHMC approval before giving the money. Once you give the money unnecessarily you will be fixed.
You should confirm the GHMC approval. Then only you should proceed.