Is It compulsory to enable billing account by June 11, 2018 through credit card information to continue to access Google Maps API?

For projects that existed prior to June 11, 2018

According to the Google Maps Platform technical support, a billing account without any credit card information will be created for each project without billing account. This means that the API calls will still succeed, as long as they fit within the free tier of $200 per month. If your application goes over the 200$ free tier, the billing account will be closed, and API calls will start failing. The only option after that to reopen billing account is entering the credit card information.

For project that were created after June 11, 2018

You must enable a billing account in order to use Google Maps APIs.