Hello,
Based on this
document after first 500,000 characters* per month free usage user will start to get a charge of $20# per million characters.
For Cloud Translation - Basic, Google charges the project that is associated with the private key that user used to make authenticated requests. For Cloud Translation - Advanced, Google bills against the project that contains the translation model that user use, not against the project that user used to make the request.
From that it appears that you have utilized the free usage and that is the reason why you have got the error "Error using google translate, service requires a paid account".
If the above is not the case, please report the issue by creating a
Cloud Translation issue under AI and Machine Learning of this
document. After that one of the Google Cloud Platform Support agent will be happy to assist you.