Hello OliviaSurgere,
Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
The mismatched_redirect_uri error response is typically caused when the redirect URI in your Authorization Request doesn't exactly match the redirect URI in your key's settings (https://app.constantcontact.com/pages/dma/portal/).
One additional thing I did want to mention as well:
While it won’t return any errors if excluded from your Authorization Request, you’ll want to also include the new scope “offline_access”, which is now required for returning refresh tokens
Like so:
scope=contact_data+campaign_data+offline_access
Here is how your initial Authorization Request URL should be formatted:
GET https:// authz.constantcontact.com/oauth2/default/v1/authorize?client_id=________________&scope=________________+offline_access&response_type=code&state=________________&redirect_uri=________________
Step 1: Create an Authorization Request
https://v3.developer.constantcontact.com/api_guide/server_flow.html#step-1-create-an-authorization-request
Please have a look and let us know if you have any other questions!
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