Hi,
I am free plan and trying to experiment with APIs. Do I need to do phone verification?
I am getting insufficient_quota error for even the very first API request.
Do I need to move to paid plan, even to start trying the APIs requests.
Regards,
Anurag
Welcome to the forum!
_j is a regular who gives correct answers.
I might be a forum regular, I might give some correct answers, but regular correct answers might be a stretch… 
But yes, you are on the right path. Especially when the error says “check your plan…”
The API is a service that is not by subscription (like ChatGPT Plus) but still must be funded, because you pay for the language data that the AI model receives and sends back with every use.
Recent brand new accounts may have been granted a $5 credit that expires after three months, but if you were using ChatGPT and only recently pondered the API, that trial grant given when you first signed up may have already expired.
Here’s a page within one’s API account for “usage”. On the right on desktop view, there will be a category “credit grants” if you’ve received one, showing the amount – and with the bar graph colored pink for the amount that has already expired.
So then, the “verification” you need is to add a payment method (accepted credit card), and prepay for some account credits to fund your API usage.
Here’s prices, BTW.
(yes, I’ve probably written the same before, but you get your own personalized response)