Non-static method zsign\ApiClient::constructErrorMessageFromAPIResponse() cannot be called statically

Non-static method zsign\ApiClient::constructErrorMessageFromAPIResponse() cannot be called statically

Hello - I sent this before but not sure you received it as I was not logged in to my account.

We get this error now when running on the server - we never used to get this error before!

Non-static method zsign\ApiClient::constructErrorMessageFromAPIResponse() cannot be called statically

We are using the package zoho-sign/php-sdk. It was working a few days ago (i.e. no error page) but now all of a sudden we get this error.