That would be submarine firing , which is to be proven and cleared for submarine firing (capital trial or something) by DRDO side of development work.
So there are different phases in terms of development. First you develop and prove the entire system based on pontoon (after all the ground based work etc) then the full system should be cleared for the platform based trials first from a simulated platform then when reliable enough (reliability & IVV independent verification & validation studies with clearance are involved at every step of the process) you finally have enough confidence for direct firing from a sub you go on. For this navy has to allow modification & installation on a sub which need to be insured obviously in case any accident. Project allocation has to provision for such fund allotment because Navy won't pay that bill so it comes from PMO probably.
Then finally the whole system ie canisters, launch tech, missile, system installation inside the sub, anti vibration fitment etc many such things are complete then firing from the sub happens. In the first 1-2 cases it is DRDO who take the lead under navy or SFC as observer. With successful firing complete and report submitted, then DRDO has to handover and train Navy/SFC/submarine grp people on the whole matter so the submariners can operate it on their own.
Then in the next stage Navy/strategic force people take over and DRDO side work becomes as technical observer and assistance ie DRDO side is no longer the lead but present there to assist with the Naval/SFC command along with the pvt vendor pool who were involved. Navy has to do the whole firing mission, they would provide DRDO with their choice of config so they can prepare the programming for proof firing. Once fired and test complete DRDO side role is to validate the test case data and match it with data gathered during the test by tracking & telemetry. This is done to check whether the missile did everything as it was programmed for.
In the last K4 test which many said was failed, the Naval chief said during a question that they fired it and now they were checking whether everything was ok. This is done by matching test data with telemetry gathered data which is DRDO side of work under lead agency Navy/SFC. The missile worked like textbook, it did its mission exactly how navy wanted it to do, made the precise maneuvers and splashdown was where they wanted it to.
Since K4 is like IRBM class, it shows we have option available not only in ICBM range naval nuke triad via K5, we have every range modulus covered from MRBM upto 1500km to IRBM K4 4000km to future K5. What is implemented in land based system is repeated for underwater system too. Conical rv perform the best with a total high payload package as its second strike option so delivery needs to be precise and heavy. It will deliver (multi) megaton equivalent overall if ever used.