Thank you for reaching out to Constant Contact's API Support.
Our v3 API is our newest version and will be including new features and products that our v2 API does not include.
Do trial users like me have permission to use API to develop and test Constant Contact sign up form?
To make a new signup form, does it require OAuth2.0 server flow. ?
What is the easiest way to create a signup script using PHP.\?
The customer wants to include Google reCAPTCHA function to form as the next step.
Any clues appreciated.
Trial users do have access to our API, please keep in mind your trial account may expire and then you will not be able to access your Constant Contact account.
Using the API for any reason, including a sign-up form, requires using the oAuth flow. We have some small code snippets of PHP under each endpoint, but it is not a full sign-up form/integration. As for adding reCaptcha I can tell you that it will work with our API. You will need to reference their documentation to ensure you write the code correctly.