rails Daily Limit for Unauthenticated Use Exceeded for qr_code

I am working in Ruby on rails application. We are using the URL Shortener API using "gem googl" and have signed up and created a project for it. We have enabled the API and have created a Public API Access key. We have whitelisted the domains that are allowed to call. We are using an individual google developer console account. Not business.

Everything worked fine the first 2 or 3 days. Then suddenly we started to get this error message every call we do:

Exception: {"error"=>{"errors"=>[{"domain"=>"usageLimits", "reason"=>"dailyLimitExceededUnreg", "message"=>"Daily Limit for Unauthenticated Use Exceeded. Continued use requires signup.", "extendedHelp"=>"http://ift.tt/nd20To"}], "code"=>403, "message"=>"Daily Limit for Unauthenticated Use Exceeded. Continued use requires signup."}}

We have google all different forums for this error. But have not found the solution.

What do we need to do?